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. 

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. 

Why Precise Dose Calculation is Critical for Low Dose Dexamethasone Suppression Testing

I just read your latest blog post on the low dose dexamethasone suppression test (LDDST) and have a couple of questions. I think many veterinarians are aware that the active dexamethasone portion of dexamethasone sodium phosphate (Dex SP) is less than what the labeled concentration states. However, I also know that some colleagues do not take the "active" dose of dexamethasone vs the total Dex SP into account. when calculating the dose administered for LDDST testing.

So, from your experience, if a veterinarian fails to take into account the fact that 1-ml of Dex SP (4 mg/ml) is really only delivering 3 mg of active dexamethasone, will the actual test results be effected or altered to a significant degree? Would it really make a clinical difference?

And you mentioned diluting the Dex SP. How do you do the dilution? Do I have to make a fresh dexamethasone dilution for every LDDST I do or can I store the diluted dexamethasone? If so, how long would this dilution be stable?

My Response:

Let me address your second question about diluting the Dex SP first, because I believe that dilution is key to giving an accurate dose. This is true in all dogs, but is mandatory in small breed dogs.

How to dilute and store dexamethasone sodium phosphate preparation for the LDDST
I routinely dilute the dexamethasone sodium phosphate (Dex SP) used for the LDDST. This is my protocol for diluting the steroid, but actually it probably can be diluted more or less as needed based upon the size of the dog.

• Draw up 1-ml of Dex SP (4 mg/ml), containing 3 mg (3,000 μg) of active dexamethasone,
• Add this 1-ml volume of Dex Sp into a sterile glass vial.
• Add 5-ml of bacteriostatic 0.9% saline to the sterile glass vial containing the 1-ml of Dex SP. 
• The concentration of the diluted Dex SP salt in the glass vial is now 0.67 mg/ml (667 μg/ml). 
• More importantly, the concentration of the diluted "active" dexamethasone is now 0.5 mg/ml (500 μg/ml).
• Store the diluted Dex SP for up to 1 month in the refrigerator (1). It's likely that this diluted Dex SP is stable for much longer than 1 month, but we just don't know how long.
• Remember to protect the diluted Dex SP from light (i.e., keep in dark refrigerator).

Diluting the Dex SP is recommended to ensure administration of the correct dose

Calculating the correct dexamethasone dose for the LDDST 
Now let me address your question: does it really matter if we calculate the dose for the LDDST based on the weight of the Dex SP salt or the actual dexamethasone contained with the salt? Again, as I discussed in my last blog post, the Dex SP label states a concentration of 4 mg/ml for the dexamethasone salt, but that is equivalent to only 3 mg/ml of active dexamethasone (2).

For an example, let's take a dog weighting 20 kg that we need to test for Cushing's syndrome with the LDDST. Let's do the dose calculations both ways — based on the weight of the dexamethasone salt and then based on the active dexamethasone:

• Remember that the dose of the LDDST test is 0.01 mg/kg (or 10 μg/kg); I find working with micrograms easier since it avoids all the tiny numbers and decimal points!
• So first, take 20 kg times 0.01 mg/kg (or 10 μg/kg) = 0.2 mg or 200 μg (the dose to inject).
• If we use the 3 mg/ml of active dexamethasone for the calculation, that means we would administer 200 μg of active dexamethasone to the patient.
• In contrast, if we use the 4 mg/ml of Dex SP salt for the calculation, that means we would administer 200 μg of Dex SP salt, but only 150 μg of active dexamethasone! This calculates out to an administered dose that contains 25% less active dexamethasone than what we should be giving.

So could it really make a difference if we calculated the dose based on the weight of the dexamethasone salt or based on the active dexamethasone contained in the Dex SP? Of course it could, and that's why it is important to carefully calculate and draw up an accurate Dex SP dose to administer when doing a LDDST.

Bottom Line: 

If we miscalculate the dose for the LDDST using the concentration of the total Dex SP salt rather than the concentration of active dexamethasone, we will administer a dose that is 25% less than is needed to ensure complete suppression of the hypothalamic-pituitary-adrenal axis (3-5). In other words, by giving a lower dexamethasone dose, it would certainly be possible to see a normal dog fail to completely suppress the serum cortisol concentrations or show "escape" from suppression at 8 hours.

In other words, if we make the calculation incorrectly, this may lead to false positive test results for Cushing's disease. And that's the last thing we want to do.

References:

1. Plumb DC. Plumb's Veterinary Drug Handbook. Seventh Edition. Wiley-Blackwell; 2011.
2. Lugo RA, Nahata MC. Stability of diluted dexamethasone sodium phosphate injection at two temperatures. The Annals of Pharmacotherapy 1994;28:1018-1019.
3. Melián C, M. Pérez-Alenza, D, Peterson ME. Hyperadrenocorticism in dogs, In: Ettinger SJ (ed): Textbook of Veterinary Internal Medicine: Diseases of the Dog and Cat (Seventh Edition). Philadelphia, Saunders Elsevier, 2010;1816-1840.
4. Peterson ME. Diagnosis of hyperadrenocorticism in dogs. Clinical Techniques in Small Animal Practice 2007;22:2-11.
5. Herrtage ME, Ramsey IK. Canine hyperadrenocorticism. In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Quedgeley, Gloucester: British Small Animal Veterinary Association; 2012:167-189.

Q & A: High Serum Estradiol in a Neutered Male Dog with Alopeica

My patient is a 2-year old male castrated Alaskan Malamute that presented with the main clinical sign of patches of nonpruritic alopecia on the dorsal lumbar area. There is no other hair loss or clinical signs. 

The serum chemistry panel, total and free T4, and TSH concentrations are all normal.

I did an ACTH stimulation test and send serum to the Clinical Endocrinology laboratory at the University of Tennessee for the adrenal sex hormone panel. These are the results, before and after ACTH stimulation:

• Cortisol — Basal value 19 ng/ml (reference range, 2-56 ng/ml) Post-ACTH 96 ng/ml (reference range, 70-151 ng/ml)
• Androstenedione — 0.15 ng/ml (reference range, 0.05-0.3 ng/ml) Post-ACTH 0.76 ng/ml (reference range, 0.24-2.0 ng/ml)
• Progesterone — Basal 0.06 ng/ml (reference range, 03-.17 ng/ml) Post-ACTH 64 ng/ml (reference range, 22-1.45 ng/ml)
• Aldosterone — Basal value 19 ng/ml (reference range, 2-56 ng/ml) Post-ACTH 96 ng/ml (reference range, 70-151 ng/ml)
• Estradiol — Basal value 85 pg/ml (reference range, 23-65 pg/ml) Post-ACTH 75 pg/ml (reference range, 23-69 pg/ml)

My question: what would be the source of the high serum estradiol concentrations? Does it mean anything?

Should I start the dog on melatonin or mitotane?

My Response:

Estradiol (17β-estradiol) is a sex hormone produced in the ovary in the female. In the intact male, estradiol is also present, being produced as an active metabolic product of testosterone (1). In neutered dogs, The adrenal glands do not secrete estradiol directly but do normally secrete adrenal androgens (i.e., androstenedione and testosterone), even in the neutered dogs. A fraction of these adrenal androgens undergoes conversion to estradiol by an enzyme called aromatase in peripheral tissues (especially fat cells).

Conversion of circulating testosterone (steroid on left) to estadiol (on right).
The enzyme aromatase transforms the left-hand ring (the A-ring) of steroids to an aromatic state (hence the name) through oxidation and subsequent elimination of a methyl group.

So the source of the circulating estradiol that you are measuring could indirectly be the adrenal glands, but whether or not the high value found in this dog is clinically significant is difficult to know. These adrenal panels are difficult to interpret, and they are often abnormal in dogs even without clear evidence of typical or atypical Cushing's syndrome (2).

In a recent study of normal dogs published out of the University of Tennessee, they showed that the there was a wide range of variability in estradiol concentration both within and between the dogs (3). In addition, they reported that these estradiol concentrations often exceed the normal ranges established by the laboratory! This may account for why most of the adrenal panels I see have an abnormal sserum estradiol concentration.

Based on that study (3), I would ignore the results of these adrenal panels when the only abnormality is a high serum estradiol concentration.

Alopecia X is a term that has been used to describe dog that show dermatological signs that look similar to that seen with Cushing's disease (e.g., bilaterally symmetric alopecia and hyperpigmentation). This syndrome is common seen in the Nordic breeds, Pomeranians, and Chow chows. The cause of alopecia X is not understood (thus the term alopecia X!), but it is associated with hair cycle arrest.  Adrenal sex hormone abnormalities are no longer believed to play a role (4-6).

Since other labs are normal and since the dog is an Arctic breed, Alopecia X is certainly possible, and a relatively benign treatment such as melatonin can be tried. Click here to see a nice website with more info for vets and owners about alopecia X in Malamutes.

References:

1. Rijnberk A. Kooistra HS. Testes, In: Clinical Endocrinology of Dogs and Cats: An Illustrated Text. Second Edition. Schluetersche 2009.
2. Behrend EN, Kennis R. Atypical Cushing's syndrome in dogs: arguments for and against. The Veterinary Clinics of North America: Small Animal Practice 2010;40:285-296.
3. Frank LA, Mullins R, Rohrbach BW. Variability of estradiol concentration in normal dogs. Veterinary Dermatology 2010;21:490-3.
4. Frank LA, Hnilica KA, Oliver JW. Adrenal steroid hormone concentrations in dogs with hair cycle arrest (Alopecia X) before and during treatment with melatonin and mitotane. Veterinary Dermatology 2004;15:278-284.
5. Frank LA, Donnell RL, Kania SA. Oestrogen receptor evaluation in Pomeranian dogs with hair cycle arrest (alopecia X) on melatonin supplementation. Veterinary Dermatology 2006;17:252-258.
6. Frank LA. Oestrogen receptor antagonist and hair regrowth in dogs with hair cycle arrest (alopecia X). Veterinary Dermatology 2007;18:63-66.