Hypothyroidism Associated with Acromegaly and Insulin-resistant Diabetes Mellitus in a Samoyed

PAPER REVIEW

Hypothyroidism Associated with Acromegaly and Insulin-resistant Diabetes Mellitus in a Samoyed

by T. Johnstone, E. Terzo, and C. Mooney

Australian Veterinary Journal 2014; 92:437-442.

Background

Although both hypothyroidism and diabetes mellitus are common disorders of dogs, it is relatively uncommon for a dog to develop both diseases concurrently. Insulin-resistant diabetes has been reported in a few dogs with underlying hypothyroidism (1-3), but the mechanisms underlying the insulin resistance is not clear. However, hypothyroidism may lead to alteration of other hormones that influence glucose metabolism, and previous studies of hypothyroid dogs have documented excessive production of growth hormone (GH), a known insulin antagonist (4,5). In one study, Beagles with radioiodine-induced hypothyroidism were reported to have a progressive elevation in serum GH concentrations (a known insulin antagonist), but none of those dogs developed overt diabetes (6).

The purpose of this case report by Johnstone et al. (7) is to describe a dog diagnosed with naturally occurring hypothyroidism that also had concurrent signs of acromegaly and diabetes. In this dog, the insulin resistance and associated diabetic state was reversed with appropriate L-thyroxine supplementation.

Case Report
A 4-year-old male entire Samoyed presented with an 8-month history of pedal hyperkeratosis and shifting lameness, which had been unresponsive to zinc supplementation, antibiotics, and glucocorticoid therapy. The dog also exhibited exercise intolerance of 12-months duration. Recently, polydipsia and polyuria were also noted.

Marked interdental spacing

On physical examination, obesity, poor coat condition, widened spaces between the teeth, and mild respiratory stridor were noted (see Figure).

Initial laboratory test results confirmed marked hyperglycemia, consistent with diabetes mellitus. Serum concentrations of total thyroxine (T4), free T4 by equilibrium dialysis, and free triiodothyronine (T3) were below the reference limits, and canine thyroid-stimulating hormone (cTSH) levels was above the reference limits, diagnostic for primary hypothyroidism.

Before treatment for diabetes and hypothyroidism was initiated, further tests were performed to investigate a potential link between these two conditions. An upper airway examination revealed mild soft tissue hypertrophy but normal laryngeal function. The pretreatment serum insulin concentration was above the reference limits, suggesting endogenous insulin resistance. A baseline serum IGF-1 concentration was within reference limits. However, basal serum GH concentrations were markedly elevated, and a further paradoxical increase in GH concentration was noted after administration of thyrotropin-releasing hormone (TRH). CT imaging of the pituitary suggested slight enlargement of the gland but no pituitary tumor was evident.

Overall, the high serum GH concentrations, together with the clinical features (e.g., widened interdental spaces, and mild respiratory stridor), was considered diagnostic for acromegaly.

Treatment was initiated using both insulin (Caninsulin, 20 IU every 12 h) and thyroid supplementation (levothyroxine, L-T4, 0.02 mg/kg every 24 h). Over the next few weeks, the exogenous insulin requirements started to decrease, and all exogenous insulin was discontinued 155 days later. The dog remained euglycemic 2 years after diagnosis, with continued daily supplementation of L-T4 alone.

My Bottom Line:

In this dog, diabetes mellitus was thought to be a secondary consequence of insulin resistance, as demonstrated by the high pretreatment serum insulin concentration. Insulin-resistant diabetes mellitus has been previously described in a few dogs with naturally occurring hypothyroidism (1-3), but the pathogenesis for the concurrent development of the two diseases is not totally understood.

It has been reported, however, that primary hypothyroidism can lead to with functional and morphological changes of the pituitary gland (4-6). Most notably, transdifferentiation of pituitary TSH-producing cells to cells producing both TSH and GH has been documented (6), which can result in increased GH production and secretion in these dogs. The high basal GH concentration and the paradoxical increase of GH after stimulation with TRH in this dog (7) confirmed that hypothyroidism-induced acromegaly and secondary diabetes was likely.

Although the true prevalence of hypothyroidism-induced acromegaly in dogs is not known, our clinical experience suggests that hypothyroidism is rarely associated with acromegaly. However, it is likely that acromegaly goes under-diagnosed in some hypothyroid dogs since many of the clinical signs of both disorders are similar. Furthermore, pituitary transdifferentiation of TSH to GH hypersecretion would be expected to take a long time to develop, and therefore, hypothyroidism-induced acromegaly may only become significant when hypothyroidism remains undiagnosed or untreated for several months to years (6).

In this dog, the fact that the diabetic state resolved during treatment with L-T4 suggests that the pituitary GH overproduction resolved as euthyroidism was achieved. Unfortunately, repeat TRH stimulation testing or serum GH measurements were not repeated after resolution of the diabetic state, so we can not say for certain that the acromegalic state truly resolved. Further studies certainly are needed to investigate hypothyroidism-induced GH production, but this interesting case certainly does add some insight to what may be going on in these dogs.

References:

1. Blois SL, Dickie E, Kruth SA, et al. Multiple endocrine diseases in dogs: 35 cases (1996-2009). J Am Vet Med Assoc 2011;238:1616-1621. 
2. Ford SL, Nelson RW, Feldman EC, et al. Insulin resistance in three dogs with hypothyroidism and diabetes mellitus. J Am Vet Med Assoc 1993;202:1478-1480. 
3. Hess RS, Saunders HM, Van Winkle TJ, et al. Concurrent disorders in dogs with diabetes mellitus: 221 cases (1993-1998). J Am Vet Med Assoc 2000;217:1166-1173. 
4. Lee WM, Diaz-Espineira M, Mol JA, et al. Primary hypothyroidism in dogs is associated with elevated GH release. J Endocrinol 2001;168:59-66. 
5. Diaz-Espineira MM, Galac S, Mol JA, et al. Thyrotropin-releasing hormone-induced growth hormone secretion in dogs with primary hypothyroidism. Domest Anim Endocrinol 2008;34:176-181. 
6. Diaz-Espineira MM, Mol JA, van den Ingh TS, et al. Functional and morphological changes in the adenohypophysis of dogs with induced primary hypothyroidism: loss of TSH hypersecretion, hypersomatotropism, hypoprolactinemia, and pituitary enlargement with transdifferentiation. Domest Anim Endocrinol 2008;35:98-111. 
7. Johnstone T, Terzo E, Mooney CT. Hypothyroidism associated with acromegaly and insulin-resistant diabetes mellitus in a Samoyed. Aust Vet J 2014;92:437-442. 

Top Endocrine Publications of 2014: The Canine and Feline Pituitary Gland

For my next review of the endocrine publications of 2014 that concern companion animals, I'm going to turn to the theme of diagnosis and treatment of pituitary problems in dogs and cats. Listed below are 18 clinical and research papers written in 2014 that deal with a variety of pituitary gland issues of clinical importance in dogs and cats.

These range from case studies of cats with primary hypodipsia and inappropriate antidiuretic hormone secretion (1,2) to an investigation of the clinical utility of formulas of estimated serum osmolality (3); from a study of acromegaly in a series German shepherd dogs (4) to a number of excellent studies of the clinical features, diagnosis, or treatment of feline acromegaly (8,9,13,15); and from investigation of the stress response in dogs (5,14) to a study of the intraoperative changes of circulating vasopressin during elective ovariohysterectomy in dogs (6).

Other publications include a study investigating the problems associated with commercial assays for determination of feline ACTH (7) to a review of the use of GnRH agonists in dogs and cats (10); from a report of a transsphenoidal surgical technique for removal of pituitary adenomas in dogs with pituitary-dependent Cushing's disease (11) to a review of the role of prolactin in canine mammary tumor development (12); and finally, from a report of the clinical findings, diagnostic test results, and treatment outcome of 30 cats with spontaneous Cushing's disease (16) to an investigation of the mutations associated with pituitary dwarfism in Saarloos and Czechoslovakian wolfdogs (18).

References:

1. Bach J, Claus K. Primary hypodipsia in a cat with severe hypernatremia. J Feline Med Surg 2014;16:240-242. 
2. Demonaco SM, Koch MW, Southard TL. Syndrome of inappropriate antidiuretic hormone secretion in a cat with a putative Rathke's cleft cyst. J Feline Med Surg 2014;16:1010-1015. 
3. Dugger DT, Epstein SE, Hopper K, et al. A comparison of the clinical utility of several published formulae for estimated osmolality of canine serum. J Vet Emerg Crit Care (San Antonio) 2014;24:188-193. 
4. Fracassi F, Zagnoli L, Rosenberg D, et al. Spontaneous acromegaly: a retrospective case control study in German shepherd dogs. Vet J 2014;202:69-75. 
5. Hekman JP, Karas AZ, Sharp CR. Psychogenic stress in hospitalized dogs: cross species comparisons, implications for health care, and the challenges of evaluation. Animals (Basel) 2014;4:331-347. 
6. Hoglund OV, Hagman R, Olsson K, et al. Intraoperative changes in blood pressure, heart rate, plasma vasopressin, and urinary noradrenalin during elective ovariohysterectomy in dogs: repeatability at removal of the 1st and 2nd ovary. Vet Surg 2014;43:852-859. 
7. Kemppainen RJ. Amino acid differences in cat adrenocorticotropin account for the inability of a human-based immunoradiometric assay to detect the molecule in cat plasma. J Vet Diagn Invest 2014;26:431-433.
8. Lamb CR, Ciasca TC, Mantis P, et al. Computed tomographic signs of acromegaly in 68 diabetic cats with hypersomatotropism. J Feline Med Surg 2014;16:99-108. 
9. Lourenco BN, Randall E, Seiler G, et al. Abdominal ultrasonographic findings in acromegalic cats. J Feline Med Surg 2014.  
10. Lucas X. Clinical use of deslorelin (GnRH agonist) in companion animals: a review. Reprod Domest Anim 2014;49 Suppl 4:64-71. 
11. Mamelak AN, Owen TJ, Bruyette D. Transsphenoidal surgery using a high definition video telescope for pituitary adenomas in dogs with pituitary dependent hypercortisolism: methods and results. Vet Surg 2014;43:369-379. 
12. Michel E, Rohrer Bley C, Kowalewski MP, et al. Prolactin--to be reconsidered in canine mammary tumourigenesis? Vet Comp Oncol 2014;12:93-105. 
13. Myers JA, Lunn KF, Bright JM. Echocardiographic findings in 11 cats with acromegaly. J Vet Intern Med 2014;28:1235-1238. 
14. Nagasawa M, Shibata Y, Yonezawa A, et al. The behavioral and endocrinological development of stress response in dogs. Dev Psychobiol 2014;56:726-733. 
15. Rosca M, Forcada Y, Solcan G, et al. Screening diabetic cats for hypersomatotropism: performance of an enzyme-linked immunosorbent assay for insulin-like growth factor 1. J Feline Med Surg 2014;16:82-88. 
16. Valentin SY, Cortright CC, Nelson RW, et al. Clinical findings, diagnostic test results, and treatment outcome in cats with spontaneous hyperadrenocorticism: 30 cases. J Vet Intern Med 2014;28:481-487. 
17. van Rijn SJ, Riemers FM, van den Heuvel D, et al. Expression stability of reference genes for quantitative RT-PCR of healthy and diseased pituitary tissue samples varies between humans, mice, and dogs. Mol Neurobiol 2014;49:893-899. 
18. Voorbij AM, Leegwater PA, Kooistra HS. Pituitary dwarfism in Saarloos and Czechoslovakian wolfdogs is associated with a mutation in LHX3. J Vet Intern Med 2014;28:1770-1774. 

What's the Best Dosage of Desmopressin when Injected Subcutaneously?

In a recent blog, you mentioned using compounded desmopressin (0.01%) that could be injected subcutaneously (SC).  I have 3 questions about the use of this desmopressin preparation:

1. What dose do you recommend for this formulation (per patient or per kg)? 
2. I've read elsewhere that the dose should be 2 µg per patient, administered once or twice daily. Would you agree with this (i.e., dosing independent of the weight of the patient)? 
3. I believe 0.01% is 100 µg/ml, correct?  If I use a U-100 insulin syringe, would this mean 2 units of the compounded formulation per dose? 

My Response:

Dose of desmopressin for SC injection
The empirical starting dose that I use for injectable desmopressin administered subcutaneously is 1–5 μg once or twice daily, depending on the size of the dog and response to therapy (1,2). As might be expected, larger-breed dogs tend to need more drug to control polyuria and polydipsia, and these bigger dogs will tolerate higher doses.

To make dosing easier, I usually have the owners draw up and administer the desmopressin with a U-100 low-dose insulin syringe. You are correct in that 0.01% is 100 µg/ml, so injecting 1-5 µg would be 1-5 units in this syringe.

Water intoxication is possible with use of this drug, so I do recommend monitoring of serum sodium concentrations, especially when high doses are given (1,3,4).

Formulations of desmopressin that can be injected
An injectable sterile solution of desmopressin acetate (4 µg/ml) marketed for intravenous use is available commercially and can be used in animals with diabetes insipidus (2). However, the cost of the injectable desmopressin is approximately 7 to 15 times higher per µg than the intranasal preparation, making this formulation cost-prohibitive for use in most dogs and cats.

The human nasal preparation of desmopressin can also be administered subcutaneously, but that preparation is not sterile and not authorized for this route (1,2).

Therefore, I generally use a compounded, veterinary, injectable formulation, which has already been sterilized by the compounding pharmacy and is safe to inject subcutaneously. This form is much cheaper than the injectable solution of desmopressin marketed for parenteral use in human patients.

References:

1. Shiel RE. Disorders of vasopressin production. In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology, Fourth ed. Gloucester: British Small Animal Veterinary Association; 2012:1-13. 
2. Peterson ME. What Drugs Do We Use to Treat Diabetes Insipidus? Insights in to Veterinary Endocrinology blog post, January 13, 2011. 
3. Robson WL. Water intoxication in patients treated with desmopressin. Pharmacotherapy 1996;16:969-970.
4. Bernstein SA, Williford SL. Intranasal desmopressin-associated hyponatremia: a case report and literature review. J Fam Pract 1997;44:203-208.

Differentiating Diabetes Insipidus from Psychogenic Polydipsia in Dogs

My problem case is a  7-year old male-neutered Labrador retriever-mix that presented to me for moderate to severe polyuria and polydipsia (PU/PD).  While doing well at home, his owner did mention he also has had some recent weight gain (current weight is 29 kg). He has a history of arthritis, which the owner is treating with some type of holistic supplementation.

I did a CBC and complete biochemistry profile, with all values being within normal range. Results of complete thyroid panel (serum T4, T3, free T4, and TSH) also showed that all values were within the reference intervals.  

Urine was collected by cystocentesis for complete urinalysis and urine culture and susceptibility. The urinalysis showed a specific gravity of 1.010, with a normal sediment; the urine culture was negative. A urine cortisol:creatinine ratio was also normal.

We next performed serial measurements for urine specific gravity over a 24-hour period. The results are listed below:

• 6:30 AM 1.028 
• 3:15 PM 1.004
• 6:15 PM 1.000
• 8:10 PM 1.005
• 6:30 AM 1.019

The water consumption measured over this 24-hour period was 96 ounces (2.9 liters), which appears to be in quite high for a dog of this weight.

On an abdominal ultrasound examination, the liver, adrenal glands, bladder, and kidneys were all found to be normal.  

At this time, I've excluded the common rule outs for PU/PD, including Cushing's disease, kidney disease, diabetes mellitus, hypercalcemia, liver disease, and hyperthyroidism. My two major rule outs are either psychogenic polydipsia or diabetes insipidus (DI).

My questions:

1. Have we sufficiently ruled out diabetes insipidus based on the higher morning urine specific gravities?
2. Could this dog still be suffering from psychogenic polydipsia?
3. Any other possibilities or suggestions?

My Response:

Differential diagnoses for
polyuria & polydipsia in dogs

Your dog certainly doesn't have complete central or nephrogenic diabetes insipidus (DI). He could have partial DI, but from the history, psychogenic polydipsia (compulsive water drinking) is a major rule out (1-3).

Whenever we see such wide fluctuations in urine specific gravity measurement, we must move a behavioral problem to near the top of our differential list.

My biggest concern is that we don't want to miss a serious cause of PU/PD, such as occult pyelonephritis— remember that you have collected urine from the bladder for culture, so it's still possible that the dog has an infection in the kidneys that is difficult to detect.

There are a number of ways we could proceed at this point, but this step-wise approach is what I'd recommend.

Step 1 — Stop all supplements: First, I'd start by stopping the holistic supplements for a couple of weeks to see if that helps.  If they are giving the dog any other drugs or supplements, they should all be discontinued, at least temporarily. It is unlikely that these supplements are the problem, but we don't always know what compounds holistic or herbal supplements contain or what effects they will have on an individual dog.

Step 2—Rule out atypical leptospirosis: If no improvement is seen after discontinuing the holistic supplements, I'd next consider leptospirosis serology and urine PCR testing (4-6). Occasionally, we see an atypical form of leptospirosis in dogs that present with a relatively acute onset PU/PD, hyposthenuria or isosthenuria, but no other laboratory abnormalities (azotemia does not generally develop in these dogs). The urine concentration defect is thought to be an acquired form of nephrogenic DI (3).

In dogs not previously vaccinated for leptospirosis, Leptospira infection can be confirmed by positive leptospirosis serology or use of molecular detection of leptospiral DNA by PCR testing of urine samples. In dogs previously vaccinated for leptospirosis, a 4-fold rise in convalescent titers is often diagnostic of the atypical form of this disease.

Step 3— Rule out occult pyelonephritis: If testing for atypical leptospirosis is negative, then I'd next do an antibiotic trial for 2 weeks to rule out occult pyelonephritis (3).

The antibiotics that I would recommend for this trial are either enrofloxacin (Baytril) at the dosage of 10 mg/kg/day or amoxicillin/clavulanic acid (Clavamox) at the dosage of 12.5 mg/kg/day. Since this is a relatively large dog, generic ciprofloxacin would be a cheaper alternative than brand-name enrofloxacin. The dose of ciprofloxacin, however, is 1.5-2 times greater than Baytril because of poorer intestinal absorption of the drug (7).

If the dog's PU/PD markedly diminishes during the antibiotic trial period, then we can make a presumptive diagnosis of occult pyelonephritis.  In that case, the antibiotic treatment would be extended for a full 6-week period.

Step 4— Do water deprivation test: If we see no clinical response to the antibiotic treatment, then I'd go on and do a water deprivation test next. The water deprivation test is generally considered by most authorities to be the best diagnostic test for differentiating between central DI, nephrogenic DI, and psychogenic polydipsia. However, the classical water deprivation test is labor-intensive, difficult to perform correctly, unpleasant for the dog, relies heavily on repeated emptying of the bladder, and can lead to untoward complications and misdiagnosis in some animals (3).

What I'd recommend in this dog is to first do an abbreviated, overnight water deprivation test. With this method, the owner walks the dog late at night to empty the bladder, and the dog is then put in a room (or a cage) overnight without access to water. The first thing the next morning (before the dog is given any food or water), the owner again walks the dog and collects a urine sample.  The urine sample should then be dropped off at your office so you can measure the urine specific gravity after the overnight water deprivation. If the sample is concentrated (> 1.030-1.035), then we can rule out partial DI, leaving us with a diagnosis of psychogenic polydipsia (1-3).

Step 5— Evaluate the response to desmopressin:  If the dog fails to adequately concentrate after the overnight water deprivation test, you could do an official, in-hospital water deprivation test. However, I'd try a desmopressin trial to evaluate the response instead (3,8).

If the desmopressin does work to control the PU/PD and to raise the urine specific gravity, that is consistent with partial DI (either central or nephrogenic DI).  On the other hand, if desmopressin fails to have any effect on the water consumption or urination in this dog, that would be most consistent with psychogenic polydipsia (compulsive water drinking).

References:

1. Dunn JK. The dog with polydipsia and polyuria In: Torrance AG, Mooney CT, eds. BSAVA Manual of Small Animal Endocrinology. 2nd ed. Shurdington, Cheltenham: British Small Animal Veterinary Association, 1998;3-9.
2. Nichols R. Polyuria and polydipsia. Diagnostic approach and problems associated with patient evaluation. Vet Clin North Am Small Anim Pract 2001;31:833-844.
3. Nichols, R., Peterson ME. Investigation of polyuria and polydipsia In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Fourth ed. Gloucester: British Small Animal Veterinary Association, 2012;215-220.
4. Harkin KR, Roshto YM, Sullivan JT. Clinical application of a polymerase chain reaction assay for diagnosis of leptospirosis in dogs. J Am Vet Med Assoc 2003;222:1224–1229
5. Greene CE, Sykes JE, Brown CA et al. Leptospirosis. In: Infectious Diseases of the Dog and Cat, 3rd edn. 2006;402–417.  
6. Van De Maele I, Claus A, Haesebrouck F, et al. Leptospirosis in dogs: a review with emphasis on clinical aspects. Vet Rec 2008;163:409–413.
7. Papich MG. Ciprofloxacin pharmacokinetics and oral absorption of generic ciprofloxacin tablets in dogs. Am J Vet Res 2012;73:1085-1091.
8. Nichols R, Hohenhaus AE. Use of the vasopressin analogue desmopressin for polyuria and bleeding disorders. J Am Vet Med Assoc 1994;205:168-173.

What's the Best Route of Administration for Desmopressin in Dogs with Diabetes Insipidus?

My patient is a 10-year old, female spayed Italian greyhound suffering from diabetes insipidus that I have been treating for several years with desmopressin, with a good overall response. I'm not certain how the diagnosis of diabetes insipidus (DI) was confirmed, however, since the dog was worked up and started on desmopressin by another veterinarian.

Initially, the dog was treated with twice daily administration of desmopressin drops (0.01%) by the intraocular route. In the past 2 years, she developed severe ocular problems (uncontrolled glaucoma) and had to have both eyes enuclueated a few months ago.

Because we could no longer use the intraocular route of administration, the owner has been giving her the desmopressin intranasally. This seemed to work initially, but now polyuria and polydipsia have returned, even with 3-times-a-day intranasal treatments. Her bloodwork remains fine, with no evidence of azotemia, hypercalcemia, or hyperglycemia. The dog is showing no clinical or laboratory signs of Cushing's syndrome, and a recent low-dose dexamethasone screening test was normal.

Is there a better way to dose the desmopressin in this case? Is there anything else I should look for or rule out in this dog other than DI?

My Response:

Well, this is a first for me. I've never had a dog that was being medicated with eye drops in which both eyes had to be removed. Wow —poor dog.

Best route of administration
I've never had a dog or cat in which intranasal administration of desmopressin was successful. Intranasal formulations of desmopressin have been available for over 40 years and remain a commonly used route of administration for human patients (1,2), but most dogs just do not tolerate it very well.  Dogs tend to sneeze out the desmopressin solution before it has a chance to be absorbed from the nasal mucosa.

I'd change to either the demopressin tablets or a compounded desmopressin injectable solution (2-4). The tablets are the most expensive option, but work well in many dogs. I find that subcutaneous admintration of the desmopressin is the most effect route of administration, which also tends to be less expensive since lower doses have to be given.

You can purchase a commercially available injectable desmopressin preparation, but it's quite expensive. I generally use a compounded desmopressin injectable (0.01%) preparation, which I purchase from Wedgewood Pharmarcy. For a 5-ml vial, my cost is about $50-60. This is the cheapest price that I can find, at least with a product that works. It's already been sterilized so you don't have to do anything but start injecting it.

Other differentials for undefined polyuria and polydipsia
There are many causes for polyuria and polydipsia in the dog, almost all of which are much more common than diabetes insipidus (DI), which is a rare disorder (Table 1). Therefore, we should always question the diagnosis of DI in the adult dog, especially if an underlying cause of the DI is not apparent (e.g.,  pituitary mass).

Differential rule outs for polyuria and polydipsia in dogs and cats,
listed from most to least common (3).

It's important to realize that many dogs with polyuria will respond, at least transiently, to desmopressin, so a positive response to the drug can never be considered 100% diagnostic for DI. For example, many dogs that I suspect having mild Cushing's disease will respond to desmopressin with a decrease in thirst and urination. I will use this treatment in some of these dogs, especially if I'm not totally convinced that the cause is really Cushing's disease, but the owners need me to do something to control the polyuria.

Continued monitoring of dogs with suspected DI is recommended
So with all dogs with suspected DI, it is always a good idea to continue to monitor them for development of another disorder which could be responsible for their polyuria and polydispia  (Table 1), even when these disorders were ruled out on initial examination.

To that end, I would recommend obtaining a complete history and physical examination every 6 to 12 months. At each of these visits, I also like to monitor a complete blood count, serum chemistry panel, and complete urinalysis with culture. In many dogs with early Cushing's disease or renal disease, the diagnosis may not be obvious when they initially present for polyuria, but with time, the primary cause will become apparent.

References:

1. Richardson DW, Robinson AG. Desmopressin. Ann Intern Med 1985;103:228-239. 
2. Vande Walle J, Stockner M, Raes A, et al. Desmopressin 30 years in clinical use: a safety review. Curr Drug Saf 2007;2:232-238. 
3. Nichols, R., Peterson ME. Investigation of polyuria and polydipsia In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Fourth ed. Gloucester: British Small Animal Veterinary Association, 2012;215-220.
4. Peterson ME. What Drugs Do We Use to Treat Diabetes Insipidus? Insights in to Veterinary Endocrinology blog post, January 13, 2011. 

Top Endocrine Publications of 2013: The Canine and Feline Pituitary Gland

As I've done for the last four years, I’ve now finished compiling a fairly extensive list of references concerning canine and feline endocrinology that were written last year (in 2013). I’ll be sharing these with you over the next few weeks, as well as reviewing a few of the best papers from my lists of clinical endocrine publications.

In this post, I am going to start off with papers that deal with the theme of diagnosis and treatment of pituitary problems in dogs and cats.

Listed below are 13 clinical and research papers written in 2013 that deal with a variety of pituitary gland issues of clinical importance in dogs and cats.

These range from studies of the pathogenesis of acromegaly (and diabetes) in cats (2) to two excellent reviews of the clinical features, diagnosis, and treatment of feline acromegaly (8,9); from a case report of a cat with pituitary adenomas secreting both ACTH and GH (12) to another case report of a cat suffering from a pituitary carcinoma causing hyperadrenocorticism (6); and from a study of the accuracy of CT and MRI for contouring the feline apparatus for radiation therapy planning (for treatment of feline acromegaly) (10) to studies validating an assay for feline ACTH determination (3).

Other publications include a case report of two dogs that presented with severe polyuria and polydipsia due to thyroid carcinoma and hyperthyroidism (1) to diabetes insipidus (DI) in a cat secondary to head trauma (11); and a report on acute iatrogenic water intoxication in cats (7) to a study of the disturbances of water metabolism (normovolemic hypernatremia) secondary to pituitary gland/hypothalamic dysfunction (13).

References:

1. Bosje T, den Hertog E, Dijksta M. Does the T4 measurement belong in the standard blood analysis in polyuria/polydipsia? Tijdschr Diergeneeskd 2013;138:230-231. 
2. Dirtu AC, Niessen SJ, Jorens PG, et al. Organohalogenated contaminants in domestic cats' plasma in relation to spontaneous acromegaly and type 2 diabetes mellitus: A clue for endocrine disruption in humans? Environ Int 2013;57-58:60-67. 
3. Eiler KC, Bruyette DS, Behrend EN, et al. Comparison of intravenous versus intramuscular administration of corticotropin-releasing hormone in healthy cats. J Vet Intern Med 2013;27: 516-521. 
4. Frischknecht M, Niehof-Oellers H, Jagannathan V, et al. A COL11A2 mutation in Labrador retrievers with mild disproportionate dwarfism. PLoS One 2013;8:e60149. 
5. Goericke-Pesch S, Georgiev P, Fasulkov I, et al. Basal testosterone concentrations after the application of a slow-release GnRH agonist implant are associated with a loss of response to buserelin, a short-term GnRH agonist, in the tom cat. Theriogenology 2013;80:65-69. 
6. Kimitsuki K, Boonsriroj H, Kojima D, et al. A case report of feline pituitary carcinoma with hypercortisolism. J Vet Med Sci 2014;76:133-138. 
7. Lee JY, Rozanski E, Anastasio M, et al. Iatrogenic water intoxication in two cats. J Vet Emerg Crit Care (San Antonio) 2013;23:53-57. 
8. Niessen SJ. Update on feline acromegaly. In Practice 2013;35:2-6. 
9. Niessen SJ, Church DB, Forcada Y. Hypersomatotropism, acromegaly, and hyperadrenocorticism and feline diabetes mellitus. Vet Clin North Am Small Anim Pract 2013;43:319-350. 
10. Nolan MW, Randall EK, LaRue SM, et al. Accuracy of CT and MRI for contouring the feline optic apparatus for radiation therapy planning. Vet Radiol Ultrasound 2013;54:560-566. 
11. Oliveira KM, Fukushima FB, Oliveira CM, et al. Head trauma as a possible cause of central diabetes insipidus in a cat. J Feline Med Surg 2013;15:155-159. 
12. Sharman M, FitzGerald L, Kiupel M. Concurrent somatotroph and plurihormonal pituitary adenomas in a cat. J Feline Med Surg 2013;15:945-952. 
13. Weingart A, Gruber AD, Kershaw O, et al. Disturbances of water metabolism in two dogs and one cat with central nervous system disorders. Schweiz Arch Tierheilkd 2013;155:463-469. 

Seizures and Bilateral Adrenal Enlargement in an Older Boxer: Insulinoma, Cushing's Disease, or Something Else?

I'm looking for some advice for Alex, a 10-year old M/N Boxer who has been a long-term patient of mine. Alex's serious medical problems started a year ago, when he had his first seizure event. Blood work following this seizure was unremarkable aside from a mild elevation in the serum alkaline phosphate activity (219 IU/L; reference range, 5-131 IU/L). Alex's owner began keeping a seizure log, and Alex had further neurological issues until 7 months ago when he suffered another tonic-clonic seizure event, which lasted approximately 3 minutes.

Following this second seizure, Alex was examined by a neurologist, who found no abnormalities on his examination. Routine blood work again showed a mild elevation in the serum alkaline phosphate with all other serum chemistry values being normal. Due to Alex's age and breed, one obvious rule-out was a brain tumor or other intracranial disease, so an MRI was performed. Fortunately, the results of Alex's MRI was normal, with no brain or pituitary masses found.

Alex did well until about 4 months ago, when he had a severe seizure lasting about 5 minutes. A week later, Alex had multiple episodes of severe weakness and disorientation. His physical examination the following day was normal, but blood work revealed a further increase in the serum alkaline phosphate activity (382 IU/L), as well as a slightly low blood glucose concentration (58 mg/dl). Alex had not eaten since the night before, but in light of his clinical signs over the past few days, we sent out a serum insulin:glucose panel, which came back as follows:

• Glucose: 61 mg/dl (reference range, 70-140 mg/dl)
• Insulin: 32.2 µU/ml (reference range, 520 µU/ml)

In light of these findings, we referred Alex for an abdominal ultrasound looking for an insulinoma. No pancreatic nodules were seen. However, bilateral adrenal enlargement was noted, and the radiologist recommended a workup for Cushing's disease. Needless to say, Alex's owners were upset and frustrated with the results and recommendations, although they were told beforehand that there was a fair chance that an insulinoma would not be visible on an ultrasound examination (even if a pancreatic islet cell tumor was there).

Despite the lack of clinical signs consistent with Cushing's disease, we performed both an ACTH stimulation test as well as a low-dose dexamethasone suppression test, both of which came back completely normal. However, at the time of this same visit, Alex's blood glucose again read low (58 mg/dl) on our glucometer so we repeated a insulin:glucose panel. The serum results again came back in the borderline range for insulinoma:

• Glucose: 64 mg/dl (reference range, 70-140 mg/dl)
• Insulin: 29.2 µU/ml (reference range, 5-20 µU/ml)

By now, I'm sure that you're thanking every deity you've ever heard of that you have reached the bottom of this case history! My question is this—do we have enough evidence to make a diagnosis of insulinoma in this dog and initiate therapy? I know most specialists require a lower blood glucose (i.e., below 60 mg/dl) before they begin to interpret glucose:insulin ratios. However, in Alex, he has had a number of slightly low glucose values with slightly high insulin readings; in light of his clinical signs, insulinoma still remains my primary differential.

As I was writing this post, I just got a call from the owner — Alex had another episode of severe weakness this morning that seemed to respond to Karo syrup applied to his gums.  As you can see, we've been through the ringer with this dog and are just hoping to get the owners some answers at this point so they can sleep a little more soundly.

Thanks very much in advance for your help and very sorry for the length of this post!

My Response:

In the face of hypoglycemia, the serum insulin level should be low, so this dog's high-normal to slightly high insulin value is inappropriate given the low blood glucose values (1-4). Many dogs suffering from insulinoma can be difficult to diagnose, since many have borderline glucose and insulin values similar to what you are describing in this dog.

Could this dog have Cushing's disease?
Hyperadrenocorticism (Cushing's disease) is a clinical diagnosis and is based primarily on the finding of compatible signs (e.g., polydipsia, polyphagia hepatomegaly, hair loss, pot-belly). In a dog suspected of suffering from Cushing's syndrome, we confirm the diagnosis by using one or more of the adrenal function tests (e.g, ACTH stimulation or low-dose dexamethasone suppression tests) (5-7).

One should never make a diagnosis of hyperadrenocorticism based on the finding of large adrenal gland size alone. Remember that the stress of any nonadrenal illness commonly leads to an overactive hypothalmic-pituitary-adrenal axis. Therefore, any dog with chronic stress or illness can develop bilateral adrenocortical hyperplasia as a physiological response. I know that some radiologists like to diagnose Cushing's disease based on adrenal gland size, but this just cannot be done using this criteria alone (5,6). Dogs with Cushing's disease certainly tend to have larger adrenal glands, but large adrenal glands alone are not diagnostic for this disease.

The way I see it, it's highly unlikely that this dog has Cushing's disease. First of all, this dog doesn't have any of the classical signs associated with glucocorticoid excess (5-7). The slightly high serum alkaline phosphatase could be secondary to Cushing's disease, of course, but there is a long list of reasons what that enzyme could be high, including primary liver or bone disease, neoplasia, and other endocrine disease (8).  The history of seizures could go along with a macrotumor of the pituitary gland, but your MRI excluded a CNS or pituitary mass as the cause of the seizures. So the obvious question is this— if this dog has Cushing's disease, how do we explain the seizures and low blood glucose values, which have NOTHING to do with Cushing's syndrome! If anything, the glucocorticoid excess associated with Cushing's can lead to mild to moderate hyperglycemia, with overt diabetes developing in 5-10% of Cushing's dogs (5,6).

So let's not get sidetracked. Let's get back to why this dog has periodic weakness and seizures. Working up and treating Alex for Cushing's syndrome, even if he does have that disease, will not help the dog's main clinical problems.

Confirming or excluding insulinoma as the cause of hypoglycemia
Insulinoma is more likely in this dog, but your blood glucose values have not been very low and your insulin levels are just above reference range limits. It would be great to collect samples during a seizure episode but that's not always possible.

This is what I would recommend: I'd fast the dog overnight at home and have the owners drop the dog off at your clinic in the morning. Then collect samples for glucose and insulin every 1-2 hours throughout the day, stopping when the blood glucose falls to below 45 mg/dl, or when the dog has signs of hypoglycemia. Then submit the sample or samples that have a low glucose for insulin determination.

Ideally, we would see clinical signs of hypoglycemia, document significant hypoglycemia (less than 55
and the lower the better) together with significant hyperinsulinemia, and then give glucose (or feed) and see the signs resolve.

If you are monitoring him and you get a blood glucose of 55 mg/dl on your in-house machine, I'd go another hour (if not symptomatic) and get another sample. If that one isn't lower, I'd continue to sample through the day but monitor closely. You don't want to do this again if possible.

If the dog isn't becoming hypoglycemic by the middle of the day, it's sometimes helpful to take the dog for a brisk walk of 5 to 10 minutes and then check a blood glucose (and insulin) concentration. This exercise can help induce hypoglycemia and hyperinsulinemia in some dogs and therefore, increasing the diagnostic yield of this prolonged fast.

Follow-up Testing and Response to Treatment on Alex:

We performed fasted "glucose curve" in our hospital as you suggested. Alex's serum glucose concentration continued to decrease throughout the day, bottoming out at 42 mg/dl (glucometer reading) after a short afternoon walk. He had minimal clinical signs but did start hypersalivating, so we stopped the test at that point. We collected blood samples for serum insulin and glucose to send out to our lab, and fed the dog. Alex ate well and the hypersalivating resolved almost immediately thereafter.

The serum results came back as follows:

• Glucose: 39 mg/dl (reference range, 70 - 140 mg/dl)
• Insulin: 52 µU/ml (reference range, 5 - 20 µU/ml)

Based on these results — severe symptomatic hypoglycemia that responding to feeding together with overt hyperinsulinemia, we made a diagnosis of insulinoma.

I am happy to report that Alex has been doing well on treatment with prednisone and an adjusted feeding schedule (many smaller meals throughout the day). To this point our spot checks in the hospital have been very normal, and the seizure episodes have resolved.

We know that we are only controlling signs of hypoglycemia in this dog and growth and metastasis of Alex's insulinoma is likely within the next few months, Due to his age, the owners have declined exploratory surgery for now and just want to control the hypoglycemia medially at this time.  

References:

1. Goutal CM, Brugmann BL, Ryan KA. Insulinoma in dogs: a review. J Am Anim Hosp Assoc 2012;48:151-163. 
2. Kintzer PP. Insulinoma and other gastrointestinal tract tumours In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012;148-155.
3. Mehlhaff CJ, Peterson ME, Patnaik AK, et al. Insulin producing islet cell neoplasms:  Surgical considerations and general management in 35 dogs. J Am Anim Hosp Assoc 1985;21:607-612. 
4. Leifer CE, Peterson ME, Matus RE. Insulin-secreting tumor: diagnosis and medical and surgical management in 55 dogs. J Am Vet Med Assoc 1986;188:60-64. 
5. Peterson ME. Diagnosis of hyperadrenocorticism in dogs. Clin Tech Small Anim Pract 2007;22:2-11. 
6. Melián CM, Pérez-Alenza D, Peterson ME. Hyperadrenocorticism in dogs In: Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine: Diseases of the Dog and Cat. Seventh ed. Philadelphia: Saunders Elsevier, 2010;1816-1840.
7. Kooistra HS, Galac S. Recent advances in the diagnosis of Cushing's syndrome in dogs. Vet Clin North Am Small Anim Pract 2010;40:259-267. 
8. Fernandez NJ, Kidney BA. Alkaline phosphatase: beyond the liver. Vet Clin Pathol 2007;36:223-233. 

My Other Blog Posts that Discuss Insulinoma and Hypoglycemia:

• http://endocrinevet.blogspot.com/search/label/Hypoglycemia

Top 10 Clinical Endocrinology Research Abstracts, Part 2

Following last week’s post, this is the next installment of my review of the "top 10 list" clinical endocrinology research abstracts presented at last month's American College of Veterinary Internal Medicine Forum.

As with last week's post, I've enlisted the help of Dr. Rhett Nichols, a well-known expert in endocrinology and internal medicine whose day-job is senior member of the veterinarian consulting service for Antech Diagnostics, the world's largest laboratory dedicated to animal health.  Rhett also serves as a consultant for the Animal Endocrine Clinic, so I talk to him almost every day about the more difficult cases I see in my practice.

In this post, we will review 3 more of these "top 10" abstracts, followed by the remaining 4 abstracts in next week's post. We hope you agree with our selections, but if you don't, remember that you can always post a comment and add your opinion.

Lobetti R, Lindquist E, Frank J, et al. Adrenal gland ultrasonography in dogs with hypoadrenocorticism. J Vet Intern Med 2013:691. 

Hypoadrenocorticism can be a life-threatening disease if not treated immediately. Although a tentative diagnosis can be made on clinical signs and laboratory findings, a definitive diagnosis can only be made on an ACTH stimulation test. Unfortunately, typical clinical signs and laboratory findings are not evident in all cases and ACTH stimulation test results are usually not immediately available. As abdominal ultrasonography is widely used, it would be ideal as a diagnostic aid for hypoadrenocorticism. To date, there are only 2 studies that have shown small adrenal glands in dogs with hypoadrenocorticism on ultrasound. The purpose of this study was to identify a reliable set of adrenal ultrasonography parameters that could be used to identify dogs with hypoadrenocorticism. The records of 81 privately owned dogs that had abdominal ultrasonography done as well as an ACTH stimulation test were retrospectively evaluated. The dogs were divided into three groups: Group 1 consisted of 37 dogs with clinical signs and/or a sonogram appearance of their adrenal glands suspicious of hypoadrenocorticism and confirmed on an ACTH stimulation test. Group 2 consisted of 19 dogs with clinical signs and/or a sonogram appearance of their adrenal glands suspicious of hypoadrenocorticism but ruled out by a normal ACTH stimulation test. Group 3 consisted of 25 dogs that had no clinical signs or biochemical evidence of hypoadrenocorticism, normal sonogram appearance of their adrenal glands, and a normal ACTH stimulation test. Descriptive statistics were used to describe the data and one-way analysis of variance with Bonferroni and Tukey-Kramer comparisons used to test for statistical differences between the groups. The level of significance was set at p < 0.05. Results showed that the median right adrenal length in Group 1-3 was 1.75 cm, 1.8 cm, and 2.03 cm, respectively. Median left adrenal length in Group 1-3 was 1.77 cm, 2.08 cm, and 2.1 cm, respectively. There was no statistical difference between the right and left adrenal gland and within groups. Median right adrenal thickness in Group 1-3 was 0.34 cm, 0.37 cm, and 0.6 cm, respectively. Median left adrenal thickness in Group 1-3 was 0.31 cm, 0.4 cm, and 0.6 cm, respectively. In both right and left measurements, groups 1 and 2 were statistically different from group 3 but there was no statistical difference between groups 1 and 2. The study concluded that the ultrasound finding of small, flattened, isoechoic adrenal glands should be an alert for possible hypoadrenocorticism, prompting additional confirmatory function testing and/or therapeutic intervention.
  

 Comments—An abdominal ultrasound is often included as part of a diagnostic work-up for various disorders and clinical complaints. The ultrasound finding of bilaterally small adrenal glands, even if unexpected, should send an alert signal regarding the possibility of underlying adrenal insufficiency (1-3).

In general, dogs with hypoadrenocorticism have thinner adrenals than dogs with diseases that mimic the disorder or healthy dogs (2). Often, the left adrenal gland is easier to find than the right adrenal gland, and the left adrenal is less than 3.2 mm in diameter in dogs with confirmed hypoadrenocorticism (2). In this study, however, there was no statistical difference between the length or thickness of the either adrenal gland between the dogs with confirmed Addison's disease and sick dogs proven not to have hypoadrenocorticism.

The Bottom Line— Sonographic evidence of bilaterally small adrenal glands is a sensitive —but not specific —marker for hypoadrenocorticsm. Such findings should be followed-up with an ACTH response test, which remains the gold standard for the definitive diagnosis of hypoadrenocorticism.

References:

1. Hoerauf A, Reusch C. Ultrasonographic evaluation of the adrenal glands in six dogs with hypoadrenocorticism. J Am Anim Hosp Assoc 1999;35:214-218. 
2. Codreanu M, Şerdean C, Fernoagă C, et al. Study concerning the importance of ultrasound examination in adrenal glands diseases in dog. Lucrari Stiintifice 2009;52:483-486. 
3. Wenger M, Mueller C, Kook PH, et al. Ultrasonographic evaluation of adrenal glands in dogs with primary hypoadrenocorticism or mimicking diseases. Vet Rec 2010;167:207-210. 

Lourenco BN, Lunn KF. Abdominal ultrasound findings acromegalic cats. J Vet Intern Med 2013:689.

Acromegaly is increasingly recognized as a cause of insulin-resistance in diabetic feline patients. This study was designed to describe the sonographic changes in the abdominal organs of acromegalic cats. Cats were included if they presented to North Carolina State University or Colorado State University from January 2002 to October 2012 with poorly controlled diabetes mellitus, IGF-1 concentrations >100 nmol/L and had an abdominal ultrasound examination (AUS) performed with report available. A control group included age-matched cats that had an AUS performed for investigation of disease unlikely to affect liver, kidneys, pancreas or adrenal glands (e.g. lower urinary tract disease). Twenty five cats were included in each group. IGF-1 concentrations in the acromegaly group ranged from >148 to 638 mmol/l. Median left and right kidney length were significantly greater in the acromegaly group compared to controls (acromegaly—left: 47.0 mm; control-left: 38.1 mm; p < 0.0001; acromegaly—right: 47.0 mm; control-right: 42.2 mm; p = 0.0003). Hepatomegaly and bilateral adrenomegaly were reported in 63% and 53% of acromegalic cats respectively, and in none of the controls. Median left and right adrenal width were significantly greater in the acromegaly group compared to controls (acromegaly—left: 5.4 mm; control-left: 3.5 mm; p < 0.0001; acromegaly—right: 5.4 mm; control-right: 3.6 mm; p < 0.0001). Median pancreatic thickness was significantly greater in acromegalic patients compared to controls (13.5 mm vs. 6.1 mm; p = 0.0003). Pancreatic changes were described in 79% of the acromegalic cats and 9% of the controls. These findings indicate that compared to non-acromegalic cats, acromegalic patients have larger kidneys, liver, adrenals and pancreas.

Comments— It is well-known that growth hormone (GH) excess in the adult animal causes soft tissue (including the viscera) to grow.  Therefore, it is not unexpected that the sonographic appearance of the kidneys, liver, pancreas, and adrenal glands are enlarged in cats with acromegaly (1-6).

The Bottom Line— Acromegaly and hyperadrenocorticism are always on the rule-out list for any diabetic cat with insulin-resistance (2,5,6). In addition, both of these disorders share sonographic similarities such as liver and adrenal gland enlargement, which sometimes creates diagnostic confusion. However, it is important to keep in mind that sonographic evidence of bilateral adrenal enlargement is a sensitive, but not specific, marker for hyperadrenocorticism.

Clues that would point toward a diagnosis of hyperadrenocorticism instead of acromegaly in cats include weight loss, lack of or only mild-to-moderate insulin-resistance, muscle wasting, dermatologic signs, a generalized poor body condition, and a normal serum IGF-1 level (6). In contrast, cats with acromegaly frequently show weight gain, severe insulin-resistance, lack of muscle wasting or dermatologic signs, a good body condition, and an elevated IGF-1 level (1-6).

References:

1. Peterson ME, Taylor RS, Greco DS, et al. Acromegaly in 14 cats. J Vet Intern Med 1990;4:192-201. 
2. Berg RI, Nelson RW, Feldman EC, et al. Serum insulin-like growth factor-I concentration in cats with diabetes mellitus and acromegaly. J Vet Intern Med 2007;21:892-898. 
3. Niessen SJ, Petrie G, Gaudiano F, et al. Feline acromegaly: an underdiagnosed endocrinopathy? J Vet Intern Med 2007;21:899-905. 
4. Peterson ME. Acromegaly in cats: are we only diagnosing the tip of the iceberg? J Vet Intern Med 2007;21:889-891. 
5. Niessen SJ. Feline acromegaly: an essential differential diagnosis for the difficult diabetic. J Feline Med Surg 2010;12:15-23. 
6. Niessen SJ, Church DB, Forcada Y. Hypersomatotropism, acromegaly, and hyperadrenocorticism and feline diabetes mellitus. Vet Clin North Am Small Anim Pract 2013;43:319-350. 

Reeve-Johnson MK, Rand JS, Vankan D, et al. Diagnosis of prediabetes in cats: cutpoints for impaired fasting glucose and impaired glucose tolerance in cats 8 years and older using ear or paw samples and a portable glucose meter calibrated for cats. J Vet Intern Med 2013:693.

Humans with fasting glucose above normal, but below diabetic, are classed as having impaired fasting glucose. Impaired glucose tolerance is diagnosed based on increased glucose concentration at 2 h after oral or iv glucose administration in a standardized test. Humans with impaired fasting glucose or impaired glucose tolerance below levels considered diabetic, are classed as prediabetic, and at high risk of developing type 2 diabetes. Human prediabetics outnumber diabetics 3-4:1. We have previously reported the upper cutpoint for casual blood glucose in cats, but tests for pre-diabetes and subclinical diabetes in cats are not well characterized, and therefore, cats are not typically diagnosed until clinical diabetes is evident. The aims were to establish cutpoints for healthy neutered cats > 8 years of age for fasting and 2 h glucose using a standardized test protocol with paw or ear samples and a portable glucose meter calibrated for feline blood. All cats were client-owned and healthy on the basis of client history, physical examination and a routine blood profile. Of the 82 cats tested (aged 8-18 years), 21 were Burmese and 61 non-Burmese (22 lean-BCS 3-5/9), 20 overweight-BCS 6-7/9; and 19 obese-BCS 8-9/9). Following >18 h fast, a catheter was inserted into the cephalic vein. After 3 h, fasting glucose was measured from the ear or paw using the Abbott AlphaTRAK. Glucose (0.5 g/kg bwt) was administered i.v. over 30s and glucose measured at 2 min and 2 h. Reference intervals were determined after Box-Cox transformation and exclusion of outliers. The cutpoints were defined as the upper limits of the 95% reference intervals. Based on a priori knowledge that overweight and obese cats have abnormal glucose tolerance, cats of BCS 7-9/9 were excluded from the fasting and 2 h reference interval calculations. Reference intervals for Burmese were pooled with non-Burmese because the percentage differences of the medians and interquartile ranges for the sub-groups were 50% and 100%, respectively. Based on the 95% reference interval, the fasting glucose cut-point for cats with BCS 6/9 (n = 44) was 6.3 mmol/L (113 mg/ dL); the associated 90% confidence interval was 6.1-6.5 mmol/L (110-117 mg/dL). 2/82 cats were classed as having impaired fasting glucose (BCS 5 and 7/9). The cutpoint for 2 h glucose established using cats with BCS 6/9 was 10.0 mmol/L (180 mg/dL) (90% confidence interval 9.1-10.8 mmol/L (164-194 mg/dL). Six of 82 cats were classed as having impaired glucose tolerance (4 with BCS 8 or 9/9 including 1 Burmese, 2 with BCS 7/9). We recommend that 6.3 mmol/l (113 mg/dL) be used as the cutpoint between normal and impaired fasting glucose, and that 10.0 mmol/L (180 mg/dL) be used as the 2-h glucose cutpoint between normal and impaired glucose tolerance in a simplified intravenous glucose tolerance test using a glucose dose of 0.5 g/kg with blood glucose measured from ear or pad samples using a portable glucose meter calibrated for feline blood. 

Comments—Humans with mild fasting hyperglycemia and/or slightly impaired glucose tolerance are classified as prediabetic and are at higher risk for type 2 diabetes mellitus (1). Interestingly, approximately 50% of human patients with diabetes go undiagnosed, and it is estimated that prediabetes is 4 times more common than is overt diabetes (1).

Until recently, little attention has been paid to the definition of prediabetes in cats, especially as it relates to blood glucose concentrations. In clinical practice, cats are not typically diagnosed until overt clinical diabetes (often severe and advanced) is evident. However, because most cats suffering from diabetes have a form similar to type 2 diabetes in people, it is likely that most cats will also go through a subclinical or prediabetic phase that goes undiagnosed (2). Obviously, better guidelines for early diagnosis of this common feline disorder is needed.

This group of investigators, lead by Jacquie Rand, have previously reported an upper cutoff value (174 mg/dl) for random blood glucose sampling that helps define the onset of pre-diabetes in cats (3). A random or casual blood glucose refers to measuring blood glucose whenever the cat arrives for an examination, so this may or may not be a fasted sample.

In this abstract, these investigators report that determination of a blood glucose concentration, measured after a prolonged fast, followed by glucose tolerance testing can act as more specific diagnostic tests for prediabetes and subclinical diabetes in cats.

The Bottom Line— Although measuring a fasted blood glucose value, followed by an IV glucose tolerance test, appear to be the best diagnostic tests for prediabetes,  performing these tests are not simple, and they are not going to be very useful in a busy clinical practice. The proper implementation of these tests involves prolonged fasting, hospitalization for several hours, intravenous catheter placement, and IV administration of 50% glucose (4).

In most clinical situations, a random blood glucose remains most practical test we have for diagnosing  early diabetes or prediabetes in cats. The finding of a random blood glucose concentration >180 mg/dl should never be ignored, even if the cat is showing no overt clinical signs.

In people, the treatment of prediabetes involves intensive lifestyle management such as weight loss or weight control, exercise, special diets, management of hypertension and dyslipidemias, and the occasional use of glucose-lowering agents such as metformin and acarbose (5,6). In the cat with suspected prediabetes, the most sensible and useful strategy to combat the risk of overt diabetes is to initiate a low-carbohydrate diet (7); if overweight or obese, this should be combined with a weight loss program.

However, in the future, if specific drugs designated for the treatment of prediabetes are developed and become available for use in cats, the rules regulating the use of these drugs may be based on strict guidelines for diagnosing prediabetes (i.e., fasting blood glucose and glucose tolerance testing).

References:

1. American Diabetes Association. Diagnosis and classification of diabetes mellitus. Diabetes Care 2012;35 (Supp 1): S64-71.
2. Rand JS, Fleeman LM, Farrow HA, et al. Canine and feline diabetes mellitus: nature or nurture? J Nutr 2004:134 (Supp 8):2072S-80S
3. Reeves-Johnson M, Rand J, Anderson S, et al. Determination of reference values for blood glucose concentration in clinically-healthy, aged cats measured with a portable glucose meter from an ear or paw sample. J Vet Intern Med 2012;36:755
4. Appleton DJ, Rand JS, Priest J, et al. Determination of reference values for glucose tolerance, insulin tolerance, and insulin sensitivity tests in clinically normal cats. Am J Vet Res 2001;62:630-636. 
5. Bloomgarden ZT. Approaches to treatment of pre-diabetes and obesity and promising new approaches to type 2 diabetes. Diabetes Care 2008;31:1461-1466.
6.  Handelsman Y, Mechanick JI, Blonde L, et al. American Association of Clinical Endocrinologists Medical Guidelines for Clinical Practice for developing a diabetes mellitus comprehensive care plan. Endocr Pract 2011;17 Suppl 2:1-53. 
7. Zoran DL, Rand JS. The role of diet in the prevention and management of feline diabetes. Vet Clin North America Small Animal Practice 2013:43:233-243.

Top 10 Clinical Endocrinology Research Abstracts Presented at the 2013 ACVIM Meeting

Last month, I spent a week in Seattle, Washington attending the the 2013 American College of Veterinary Internal Medicine Forum.  As part of that meeting, a number of research abstracts were presented (oral and poster presentations) that dealt with various aspects of canine and feline endocrinology. I plan to spend the next three blogs discussing some of the newest and best research findings featured at the ACVIM meeting.

Of all of the excellent endocrine research abstracts presented, I've selected a "top 10 list" of the ones that have the most potential to change what I do in my clinical practice.  To do this, I've enlisted the help of Dr. Rhett Nichols, a well-known expert in endocrinology and internal medicine whose day-job is senor member of the veterinarian consulting service for Antech Diagnostics, the world's largest laboratory dedicated to animal health.  However, since Rhett also serves as a consultant for the Animal Endocrine Clinic (my practice), it was not that difficult to get him involved in this project!

In this post, we will review 4 of these top 10 abstracts, followed by the remaining 6 in the upcoming 2 posts. We hope you agree with our selections, but if you don't, remember that you can always post a comment and add your opinion.

Niessen S, Scudder C, Forcada Y, et al. Pasireotide (SOM230) opens doors to medical management of feline hypersomatotropism. J Vet Intern Med 2013:685.

Feline hypersomatotropism (HS) appears to be a significant cause of feline diabetes mellitus. However, successful treatment of HS is currently challenging. Radiotherapy and hypophysectomy seem the only effective therapeutic modalities, yet come with significant disadvantages. Medical options would be desirable although somatostatin (sst) analogues and dopamine agonists have thus far proven largely ineffective. Pasireotide (SOM230), a novel multi-receptor ligand sst analogue with high binding affinity for sst receptor subtypes 1, 2, 3 and 5 has been shown to suppress growth hormone (GH) and insulin-like growth factor-1 (IGF-1) in rodents as well as humans suðering from HS. Additionally, direct and indirect anti-tumor activity has been observed in vitro including sst receptor-mediated apoptosis and anti-angiogenesis. The current study aimed to assess the potential of SOM230 as a treatment modality for naturally occurring feline HS. Feline HS was diagnosed in eight diabetic cats by documenting serum IGF-1 concentration >1000 ng/ml (radioimmunoassay) and presence of a pituitary enlargement (computed tomography). On day 1 and 5, serum IGF-1 concentration was established and glycemic control assessed using a 12-hour blood glucose (BG) curve, measuring BG every 2 hours. On day 2, 3 and 4, the cats were injected with 0.03 mg/kg SOM230 s.c. BID. The initial insulin dose was dictated by the choice of the attending clinician, although was reduced according to regular BG measurements during the treatment period to avoid hypoglycemia. Pre- and post-treatment IGF-1, average 12-hour BG and insulin dose were compared using a paired t-test (significance at P < 0.05). All eight cats showed a significant decrease in serum IGF-1 (mean+/-SD day 1: 1884 + /-218 ng/ml; day 5: 1169 + /-395 ng/ ml, p = 0.001) and average 12-hour BG (day 1: 20 + /-5 mmol/l; day 5: 13 + /-4 mmol/l; p = 0.002). A significant insulin dose reduction was necessary in all cats (day 1: 10.8 + /-6 iu/injection; day 5: 3.1 + /-2 iu/injection; p = 0.015). No side effects were noticed during or after the 3 day treatment period, apart from hypoglycemia in one cat, which resolved after provision of food and reduction of insulin dose. The current study indicates that SOM230 is able to rapidly decrease GH and IGF-1 concentrations in feline HS. This, therefore, suggests that sst receptors are present in most feline somatotrophinomas, which has previously been unclear given the disappointing results during somatostatins and sst analogue therapy attempts. A return of insulin sensitivity was seen, enabling improved glycemic control to be established with reduced doses of exogenous insulin in all cats. In light of these results, a clinical trial with a longer-acting formulation of SOM230 is currently being conducted to establish long-term effects and potential for diabetic remission. 

Comments— Pasireotide (SOM230, trade name Signofor, Novartis) is an orphan drug approved for the treatment of Cushing’s disease in adult human patients when surgery has failed or is not an option (1). The drug is a somatostatin analog that targets multiple somatostatin receptors with high affinity. The result is apoptosis of those cells that produce ACTH, with significant lowering of plasma ACTH levels (2,3).

In addition, pasireotide has been shown to suppress GH and IGF -1 in rodents and human patients with acromegaly (4). Moreover, recent results of a phase III study of human patients with acromegaly treated with a long-acting release form of pasireotide show that this novel form of therapy is significantly more effective than the current standard therapy with octreotide (5).

This study by Niessen et al indicates that pasireotide is able to rapidly decrease GH and IGF-1 concentrations in feline acromegaly and suggests that somatostain receptors are present in most cats with pituitary tumors that produce excessive GH. In light of these results, a clinical trial with the long-acting release form of pasireotide is currently being conducted to establish long-term effects and potential for diabetic remission in cats with acromegaly.

The Bottom Line—It is great to finally have a medical treatment that may actually work for cats with acromegaly. Unfortunately, administration of pasireotide SC twice daily may not be a practical or affordable therapeutic option for many of our cat owners.

References:

1. Signifor Official Site - Signifor® (pasireotide) Injection. Signifor.US‎. 
2. Colao A, Petersenn S, Newell-Price J, et al. A 12-month phase 3 study of pasireotide in Cushing's disease. N Engl J Med 2012;366:914-924. 
3. McKeage K. Pasireotide: a review of its use in Cushing's disease. Drugs 2013;73:563-574. 
4. Petersenn S, Farrall AJ, Block C, et al. Long-term efficacy and safety of subcutaneous pasireotide in acromegaly: results from an open-ended, multicenter, Phase II extension study. Pituitary 2013. DOI 10.1007/s11102-013-0478-0 
5. Colao A, Bronstein M, Freda P, et al. Pasireotide LAR is significantly more effective than octreotide LAR at inducing biochemical control in patients with acromegaly: Results of a 12-month randomized, double-blind, multicenter, Phase III study. Joint 15th International Congress of Endocrinology and 14th European Congress of Endocrinology. Abstract #OC1.1. 2012 

De Marco V, Noronha KSM, Casado TC, et al. Therapy of canine hyperlipidemia with bezafibrate. J Vet Intern Med2013;27:694.

The primary and secondary hyperlipidemia are common in dogs and its treatment is necessary to prevent clinical complications such as pancreatitis, seizures, liver disease and diabetes. The therapy of mild hyperlipidemia comprising a fat restricted diet, but in more severe cases pharmacological treatment is necessary. Bezafibrate (BZF) is effective in the treatment of hypertriglyceridemia in humans, however there are no clinical studies in dogs. The objectives of this study were to assess the efficacy of BZF in reducing serum triglyceride (TG) and cholesterol (CHO) in hyperlipidemic dogs, identify a therapeutic protocol for this drug and assess possible side eðects such as muscle pain, emesis, diarrhea and elevated CK and TGP levels. Only animals with moderate to severe hypertriglyceridemia (TG> 350 mg/dL) were treated with BZF every 24 hours for 30 days before introduction of any other therapy according to the protocol: tablet 200 mg for dogs weighting less than 12 kg, tablet 200 mg for dogs weighing between 13 and 25 kg, 1 tablet 200 mg for dogs weighing over 25 kg. We studied 46 dogs (26 females and 20 males) with a mean age of 9 years. Fifteen dogs (32.6%) had primary hyperlipidemia and 31 (67.4%) secondary hyperlipidemia, which included hyperadrenocorticism (41.3%), hypothyroidism (15.2%) and chronic corticoideterapia (10.8%). All 46 (100%) dogs had hypertriglyceridaemia and 33 (71.7%) had both hypertriglyceridaemia and hypercholesterolemia. After 30 days using BZF, normalization of serum TG (TG <150 mg/dL) was observed in 91.3% of cases (n = 42/46) and of CHO (CHO < 270 mg/dL) in 66 7% (n = 22/33) of cases. Means and standard deviations of serum TG and COL before (752 ± 663 mg/dL and 428 ± 217 mg/dL) and after therapy (110 ± 82 and 244 ± 71 mg /dL) were significantly lower (p < 0.005, paired Student t test). The bezafibrate dose most used with a 95% confidence interval was 5.3 to 6.1 mg/kg (range: 4–10 mg/kg). No side effects were observed, and there was no statistical difference between the values of ALT and CK before and after therapy. It can be concluded that bezafibrate is a safe and effective drug for the canine hyperlipidemia therapy.
  

Comments—Bezafibrate is a fibrate drug used for the treatment of hyperlipidemia (1-3). In people, fibrates are used as an accessory drug in many forms of hypercholesterolemia, usually along with statins. Bezafibrate helps lower cholesterol and triglycerides in the blood and increase high density lipoproteins (HDL). The main toxicity is hepatic, myopathy, and rarely rhabomyolysis.

Hyperlipidemia is a relatively commonly recognized disorder in dogs but management can be frustrating (4). In this study, 46 dogs with primary or secondary hyperlipidemia (diabetes mellitus, Cushing’s syndrome. hypothyroidism) were treated with bezafibrate once a day over a 30-day period; triglycerides and cholesterol were significantly lowered in the majority of dogs. In addition, there was no evidence of untoward side effects (e.g., no clinical issues and ALT and CK levels were not altered).

There are 2 preparations of bezafibrate available: 200 mg tablets and 400 mg sustained-release tablets. The sustained-release preparation is taken once a day; the non-sustained release tablets are taken with each meal. For dogs, the average dose used in this study was 5 to 6 mg/kg once a day. The dosing protocol was ¼ of a 200 mg tablet for dogs < 12 kg, ½ of a 200 mg tablet for dogs weighing between 12 and 25 kg, and one 200 mg tablet for dogs > 25 kg.

The Bottom Line—Bezafibrate given once a day appears to be a safe and effective drug for the treatment of hyperlipidemia in the dog.

References:

1. Goa KL, Barradell LB, Plosker GL. Bezafibrate. An update of its pharmacology and use in the management of dyslipidaemia. Drugs 1996;52:725-753.  
2. Goldenberg I, Benderly M, Goldbourt U. Update on the use of fibrates: focus on bezafibrate. Vasc Health Risk Manag 2008;4:131-141.  
3. Teramoto T, Shirai K, Daida H, et al. Effects of bezafibrate on lipid and glucose metabolism in dyslipidemic patients with diabetes: the J-BENEFIT study. Cardiovasc Diabetol 2012;11:29. 
4. Xenoulis PG, Steiner JM. Lipid metabolism and hyperlipidemia in dogs. Vet J 2010;183:12-21.

Salesov E, Boretti FS, Sieber-Ruckstuhl NS, et al. Urinary and plasma catecholamine and metanephrine in dogs with pheochromocytoma, hyperadrenocorticism and in healthy dogs. J Vet Intern Med 2013 27:688-689.

Pheochromocytoma (PHEO) is a rare malignant catecholamine-secreting tumor of the adrenal medulla. Catecholamines and metanephrines in plasma and in 24-h urine are approved biomarkers for the detection of the disease in humans, however, the question which of the tests is best is controversial. We previously demonstrated that measurement of urinary catecholamine and metanephrine to creatinine ratios is helpful for the diagnosis of PHEO in dogs and that urinary normetanephrine to creatinine ratio may be the best test to discriminate between PHEO and hypercortisolism (HC). Knowledge on plasma catecholamines and metanephrines in dogs is scarce and no comparison between urinary and plasma parameters has been performed. The objective of the study was to measure urinary as well as plasma catecholamines and metanephrines in dogs with PHEO, HC and in healthy dogs and to determine the test with the least overlap between the group. Six dogs with PHEO, 9 dogs with HC (6 with ATH, 3 with PDH) and 10 healthy dogs were included. Urine samples were collected into HCL containing tubes to ensure a pH 2, blood samples were collected on ice, centrifuged at 4°C and immediately snap frozen in liquid nitrogen. All samples were stored at – 80°C. Urinary epinephrine (U-Epi), norepinephrine (U-Norepi), metanephrine (U-Meta) and normetanephrine (U-Normeta), and epinephrine (P-Epi), norepinephrine (P-Norepi), free and total metanephrine (PF-Meta and PT-Meta) and free and total normetanephrine (PF-Normeta and PT-Meta) were analysed by HPLC. Urinary catecholamines and metanephrines were expressed as ratios to urine creatinine concentrations. Data were analysed by non-parametric tests (P < 0,05). Similar to our previous findings U-Epi, U-Norepi, U-Meta and U-Normeta were significantly higher in dogs with PHEO and U-Norepi and U-Normeta were significantly higher in dogs with HC compared to healthy dogs. Comparison between dogs with HC and dogs with PHEO revealed significantly higher U-Meta and U-Normeta in the latter group. U-Normeta was the only parameter with no overlap. In dogs with PHEO P-Norepi, PF-Meta, PT-Meta, PF-Normeta, PT-Normeta were significantly higher and in dogs with HC P-Norepi, PF- Normeta and PT-Normeta were significantly higher than in healthy dogs. Comparison between dogs with HC and dogs with PHEO showed significant higher PF-Meta, PT-Meta, PF- Normeta, PT-Normeta in the PHEO group. Overlap was present with all 4 parameters, but was least with PF-Normeta and PT-Normeta. According to our results U-Normeta, PF- Normeta and PT-Normeta are valuable parameters for the diagnosis of PHEO, so far U-Normeta performed better than the plasma parameters. 

Comments—In some recent studies, up to one in five adrenal tumors has been a pheochromocytoma. In the past, a presumptive diagnosis of a pheochromocytoma was based on history which was often a vague, sometimes episodic description of illness, documentation of hypertension, an adrenal mass noted on abdominal ultrasound, and ruling out adrenal-dependent Cushing’s syndrome with an endogenous ACTH level or the results of dexamethasone suppression testing. This current research adds additional data to the idea that measurement of urinary and plasma catecholamine and metanephrine can also be used to aid in diagnosis.

The Bottom Line—Currently, a urine normetaphrine/creatinine level, appears to be the most sensitive and specific test to document a pheochromocytoma.  This test requires that the urine sample is acidified at the time of collection and a control urine sample from a normal dog (also acidified) is submitted. A urine normetaphrine/creatinine level at least 4-times the control is consistent with pheochromocytoma.

In the US, the test for urine normetaphrine/creatinine can be performed at Marshfield Labs (www.marshfieldlabs.com). Acid pellets for urinary acidification are available from the laboratory.

References:

1. Quante S, Boretti FS, Kook PH, et al. Urinary catecholamine and metanephrine to creatinine ratios in dogs with hyperadrenocorticism or pheochromocytoma, and in healthy dogs. J Vet Intern Med 2010;24:1093-1097. 
2. Kook PH, Grest P, Quante S, et al. Urinary catecholamine and metadrenaline to creatinine ratios in dogs with a phaeochromocytoma. Vet Rec2010;166:169-174. 
3. Kook PH, Boretti FS, Hersberger M, et al. Urinary catecholamine and metanephrine to creatinine ratios in healthy dogs at home and in a hospital environment and in 2 dogs with pheochromocytoma. J Vet Intern Med2007;21:388-393. 

Sangster K, Panciera JL, Abbott A, et al. Cardiac biomarkers in hyperthyroid cats. J Vet Intern Med 2013:637. 

Differentiation of hyperthyroid heart disease from primary myocardial disease is challenging. The cardiac biomarkers NT- proBNP and troponin I (cTNI) have proven useful in identifying cats with myocardial disease and may provide a method by which hypertrophic cardiomyopathy (HCM) and hyperthyroid heart disease can be discriminated. The primary purpose of this study was to compare plasma concentrations of NT-proBNP and cTNI in three groups of cats: cats with naturally occurring hyperthyroidism, cats with primary cardiomyopathy, and healthy older cats to determine if biomarkers differ between groups and if bio-marker concentrations in hyperthyroid cats change after resolution of the thyroid disease. We prospectively evaluated 61 client-owned cats: 23 hyperthyroid cats, 19 cats with HCM without congestive heart failure, and 19 euthyroid, normotensive healthy cats eight years of age or older. Fourteen of the hyperthyroid cats were re-evaluated three months after administration of I-131. A complete history, physical examination, CBC, serum biochemistries, urinalysis, blood pressure measurement, serum T4 concentration, plasma concentrations of NT-proBNP and cardiac troponin I, and echocardiography was obtained for each cat. Hyperthyroid and HCM cats had plasma NT-proBNP and cTNI concentrations that were significantly greater than healthy older cats, but there was no significant difference between hyperthyroid and HCM cats with respect to concentration of either biomarker. Plasma NT-proBNP and cTNI concentrations decreased in each cat that was examined three months after I-131 treatment. Plasma cTNI was within the reference interval for all cats at the three month recheck. Severely thickened myocardium persisted in one formerly hyperthyroid cat at the three month recheck, and this cat’s plasma NT-proBNP remained elevated. Although there may be a role for NT-proBNP in monitoring the cardiac response to treatment of hyperthyroidism, neither NT-proBNP nor cTNI can be used to distinguish hyperthyroid cats from cats with HCM. Therefore, the thyroid status of older cats should be ascertained prior to interpreting results of cardiac biomarker testing.
  

 Comments—Although it is well established that hyperthyroid cats will commonly develop secondary heart disease (1), it can sometimes be difficult to distinguish thyroid-induced cardiac disease from primary myocardial disease (cardiomyopathy). Over the last few years, a number of studies have confirmed the usefulness of plasma cardiac biomarkers (especially N-terminal pro-brain natriuretic peptide or NT-proBNP) to help detect hypertrophic cardiomyopathy in cats and to distinguish primary cardiac from non-cardiac causes of dyspnea in cats (2-5). Previous studies have found that hyperthyroid cats can have high circulaing levels of either troponin I or NT-proBNP; both biomarkers fall after successful treatment of the hyperthyroid state (6,7).

This research study confirmed that hyperthyroid cats can have high plasma NT-proBNP and troponin I (cTNI) concentrations, which decreased after I-131 treatment. However, there was no significant difference between hyperthyroid and HCM cats with respect to concentration of either biomarker.

The Bottom Line— Although hyperthyroid cats can have high plasma NT-proBNP and cTNI concentrations, there was no significant difference between hyperthyroid and HCM cats with respect to concentration of either biomarker. Therefore, neither of these cardiac biomarkers can be used to distinguish hyperthyroid cats from cats with HCM. Since hyperthyroidism can result in high levels of both biomarkers (6,7), the thyroid status of older cats should always be ascertained prior to interpreting results of cardiac biomarker testing.

References:

1. Syme HM. Cardiovascular and renal manifestations of hyperthyroidism. Vet Clin North Am Small Anim Pract 2007;37:723-743, vi. 
2. Wells SM, Sleeper M. Cardiac troponins. J Vet Emerg Crit Care 2008;18:235–245. 
3. Boswood A. Biomarkers in cardiovascular disease: beyond natriuretic peptides. J Vet Cardiol 2009;11 Suppl 1:S23-32. 
4. Fox PR, Oyama MA, Reynolds C, et al. Utility of plasma N-terminal pro-brain natriuretic peptide (NT-proBNP) to distinguish between congestive heart failure and non-cardiac causes of acute dyspnea in cats. J Vet Cardiol 2009;11 Suppl 1:S51-61. 
5. Wess G, Daisenberger P, Mahling M, et al. Utility of measuring plasma N-terminal pro-brain natriuretic peptide in detecting hypertrophic cardiomyopathy and differentiating grades of severity in cats. Vet Clin Pathol 2011;40:237-244. 
6. Connolly DJ, Guitian J, Boswood A, et al. Serum troponin I levels in hyperthyroid cats before and after treatment with radioactive iodine. J Feline Med Surg 2005;7:289-300. 
7. Menaut P, Connolly DJ, Volk A, et al. Circulating natriuretic peptide concentrations in hyperthyroid cats. J Small Anim Pract 2012;53:673-678.