Low-Dose ACTH Stimulation Testing in Cats

Cortisol and Aldosterone Response to Various Doses of Cosyntropin in Healthy Cats

Amy E. DeClue, Linda G. Martin, Ellen N. Behrend, Leah A. Cohn, David I. Dismukes, and Hollie P. Lee

Journal of the American Veterinary Medical Association 2011;238:176-182. 

Adrenocorticotropic hormone (ACTH) stimulation testing is commonly used to evaluate adrenocortical function in both dogs and cats (1-3). In cats, ACTH stimulation testing has been used primarily to test adrenocortical production of cortisol (4-6), but has also been used to evaluate the adrenal sex steroid (progestins and androgens) response (7-10).

Although the primary regulators of aldosterone secretion are the renin-angiotensin system and extracellular potassium concentration (11,12), ACTH acts as an additional stimulant (13). In accord with that fact, administration of exogenous ACTH to cats has been reported to cause a reliable increase in aldosterone secretion. Therefore, ACTH stimulation testing can also be used for evaluation of adrenal mineralocorticoid function (14).

Traditionally, a standard dose of cosyntropin (125 μg/cat, IV) has been recommended for ACTH stimulation testing (5). A previous study (15) documented that lower doses of cosyntropin will stimulate maximal cortisol secretion in cats. However, that study used per-cat dosing as opposed to per-body-weight dosing and did not evaluate the serum aldosterone response to ACTH stimulation.

The purpose of the study reported here by DeClue et al (16) were to determine the lowest dose of cosyntropin (Cortrosyn) on a per-body-weight basis that would produce maximal cortisol and aldosterone secretion in cats.  A secondary purpose was to determine the ideal timing of blood sample collection for cortisol and aldosterone concentrations after ACTH injection in these healthy cats.

Objective—To determine the lowest dose of cosyntropin on a per body weight basis that would produce maximal cortisol and aldosterone secretion and the ideal timing of blood sample collection after ACTH stimulation in healthy cats.

Design—Randomized crossover trial.

Animals—7 adult sexually intact male purpose-bred cats.

Procedures—Each cat received saline (0.9% NaCl) solution (control) and 5 doses (125 μg/cat and 10, 5, 2.5, and 1 μg/kg) of cosyntropin IV with a 2-week washout period between treatments. Blood samples were obtained before (baseline) and at 15, 30, 45, 60, 75, and 90 minutes after administration of saline solution or cosyntropin.

Results—Serum cortisol and aldosterone concentration increased significantly, compared with baseline values, after administration of all cosyntropin doses. Lower doses of cosyntropin resulted in an adrenocortical response equivalent to the traditional dose of 125 μg/ cat.

The lowest doses of cosyntropin that stimulated a maximal cortisol and aldosterone response were 5 and 2.5 μg/kg, respectively. Lower doses of cosyntropin resulted in a shorter interval between IV administration of cosyntropin and peak serum cortisol and aldosterone concentrations.

Conclusions and Clinical Relevance—Low-dose ACTH stimulation testing with IV administration of cosyntropin at 5 μg/kg followed by blood sample collection at 60 to 75 minutes resulted in concurrent peak serum cortisol and aldosterone concentrations that were equivalent to those achieved following administration of cosyntropin at 125 μg/cat, the standard dose currently used.

My Bottom Line:

This study confirms our earlier work that low doses of ACTH (e.g., 5 μg/kg body weight of cosyntropin) will maximally stimulate cortisol secretion in cats (15). In the cats of this study, as in our previous study, lower doses of cosyntropin resulted in an adrenocortical response that was equivalent to the traditional dose of 125 μg/cat (15, 16). The efficacy of of this low-dose ACTH stimulation testing protocol is also well documented in dogs (17-19), and has become a widely used testing dosage in clinical practice for evaluation of both hyper- and hypoadrenocorticism.

Based on the results of these cat studies, the following test protocol can be recommended:

1. Collect blood sample for basal cortisol (± aldosterone or sex steroids).
2. Calculate the cosyntropin (Cortrosyn) dosage (5 μg/kg of cat's body weight). To draw up this amount, it's best to reconstitute and dilute the Cortrosyn powder and store the remaining ACTH product (20).
3. Administer the cosyntropin dose to the cat by the IV route.
4. Collect a post-ACTH blood sample at 60-75 minutes after cosyntropin injection.

It is extremely important to point out that cosyntropin must be administered by the IV route in cats, especially when this low-dose protocol is used for ACTH stimulation testing. When given intramuscularly (IM) to cats, cosyntropin is not well absorbed and will not produce a maximal adrenocortical response (21). In cats, ACTH given by the IV route induces a greater and more prolonged adrenocortical stimu­lation than intramuscular administration.

This difference in the cortisol response between IV and IM administration is in contrast to the situation in dogs, in which IV or IM low-dose ACTH stimulation protocols produce similar adrenocortical responses (22). This difference between cats and dogs should not surprise us— we all know that cats are not just small dogs, especially when it comes down to endocrinology!

References:

1. Behrend EN, Kemppainen RJ. Diagnosis of canine hyperadrenocorticism. Vet Clin North Am Small Anim Pract 2001;31:985-1003.
2. Church DB. Canine hypoadrenocorticism In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Fourth ed. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012;156-166.
3. 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.
4. Peterson ME, Greco DS, Orth DN. Primary hypoadrenocorticism in ten cats. J Vet Intern Med 1989;3:55-58. 
5. Duesberg C, Peterson ME. Adrenal disorders in cats. Vet Clin North Am Small Anim Pract 1997;27:321-347. 
6. Peterson ME. Feline hyperadrenocorticism In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Fourth ed. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012;199-203.
7. DeClue AE, Breshears LA, Pardo ID, et al. Hyperaldosteronism and hyperprogesteronism in a cat with an adrenal cortical carcinoma. J Vet Intern Med 2005;19:355-358. 
8. Briscoe K, Barrs VR, Foster DF, et al. Hyperaldosteronism and hyperprogesteronism in a cat. J Feline Med Surg 2009;11:758-762. 
9. Quante S, Sieber-Ruckstuhl N, Wilhelm S, et al. Hyperprogesteronism due to bilateral adrenal carcinomas in a cat with diabetes mellitus. Schweiz Arch Tierheilkd 2009;151:437-442. 
10. Meler EN, Scott-Moncrieff JC, Peter AT, et al. Cyclic estrous-like behavior in a spayed cat associated with excessive sex-hormone production by an adrenocortical carcinoma. J Feline Med Surg 2011;13:473-478. 
11. Gogerly RL, Coghlan JP, Morgenroth P, et al. A compartmental model of acute stimulation of aldosterone secretion in vivo by potassium and ANG II. Am J Physiol 1993;265:E190-196. 
12. Pratt JH. Role of angiotensin II in potassium-mediated stimulation of aldosterone secretion in the dog. J Clin Invest 1982;70:667-672. 
13. Crabbe J, Reddy WJ, Ross EJ, et al. The stimulation of aldosterone secretion by adrenocorticotropic hormone (ACTH). J Clin Endocrinol Metab 1959;19:1185-1191. 
14. Zimmer C, Horauf A, Reusch C. Ultrasonographic examination of the adrenal gland and evaluation of the hypophyseal-adrenal axis in 20 cats. J Small Anim Pract 2000;41:156-160. 
15. Peterson ME, Kemppainen RJ. Dose-response relation between plasma concentrations of corticotropin and cortisol after administration of incremental doses of cosyntropin for corticotropin stimulation testing in cats. Am J Vet Res 1993;54:300-304. 
16. DeClue AE, Martin LG, Behrend EN, et al. Cortisol and aldosterone response to various doses of cosyntropin in healthy cats. J Am Vet Med Assoc 2011;238:176-182. 
17. Frank LA, Oliver JW. Comparison of serum cortisol concentrations in clinically normal dogs after administration of freshly reconstituted versus reconstituted and stored frozen cosyntropin. J Am Vet Med Assoc 1998;212:1569-1571. 
18. Kerl ME, Peterson ME, Wallace MS, et al. Evaluation of a low-dose synthetic adrenocorticotropic hormone stimulation test in clinically normal dogs and dogs with naturally developing hyperadrenocorticism. J Am Vet Med Assoc 1999;214:1497-1501. 
19. Lathan P, Moore GE, Zambon S, et al. Use of a low-dose ACTH stimulation test for diagnosis of hypoadrenocorticism in dogs. J Vet Intern Med 2008;22:1070-1073. 
20. Peterson ME. How to extend your supply of cortrosyn and lower the cost of ACTH stimulation testing. Insights into Veterinary Endocrinology, Blog post, March 22, 2011.
21. Peterson ME, Kemppainen RJ. Comparison of intravenous and intramuscular routes of administering cosyntropin for corticotropin stimulation testing in cats. Am J Vet Res 1992;53:1392-1395. 
22. Behrend EN, Kemppainen RJ, Bruyette DS, et al. Intramuscular administration of a low dose of ACTH for ACTH stimulation testing in dogs. J Am Vet Med Assoc 2006;229:528-530. 

Top Endocrine Publications of 2011: The Feline Adrenal Gland

In my eighth compilation of the canine and feline endocrine publications of 2011, I’m moving on to disorders of the feline adrenal gland.

Listed below are 6 research papers written in 2011 that deal with adrenal gland issues of clinical importance in cats.

These range from an investigation of the plasma cortisol and aldosterone responses to various doses of cosyntropin (1) to a review of primary hyperaldosteronism or Conn's syndrome (2); from the effects of FIV infection on the feline pituitary-adrenal axis (3) to a case report of a cat with "atypical" Addison's disease (4); and finally, from a review of the current thinking about critical illness-related corticosteroid insufficiency to a report of a cat with a sex hormone-secreting adrenal carcinoma (6).

References:

1. DeClue AE, Martin LG, Behrend EN, et al. Cortisol and aldosterone response to various doses of cosyntropin in healthy cats. J Am Vet Med Assoc 2011;238:176-182. 
2. Djajadiningrat-Laanen S, Galac S, Kooistra H. Primary hyperaldosteronism: expanding the diagnostic net. J Feline Med Surg 2011;13:641-650. 
3. Gomez NV, Castillo VA, Gisbert MA, et al. Immune-endocrine interactions in treated and untreated cats naturally infected with FIV. Vet Immunol Immunopathol 2011;143:332-337. 
4. Hock CE. Atypical hypoadrenocorticism in a Birman cat. Can Vet J 2011;52:893-896. http://www.ncbi.nlm.nih.gov/pubmed/22294798
5. Martin LG. Critical illness-related corticosteroid insufficiency in small animals. Vet Clin North Am Small Anim Pract 2011;41:767-782.
6. Meler EN, Scott-Moncrieff JC, Peter AT, et al. Cyclic estrous-like behavior in a spayed cat associated with excessive sex-hormone production by an adrenocortical carcinoma. J Feline Med Surg 2011;13:473-478. 

Low-Dose, Twice-Daily Trilostane Treatment for Dogs with Hyperadrenocorticism

Evaluation of Twice-Daily Lower-Dose Trilostane Treatment Administered Orally in Dogs with Naturally Occurring Hyperadrenocorticism

Edward C. Feldman

Journal of the American Veterinary Medical Association 2011;238:1441–1451.

Since first approved for use in dogs by the FDA in 2009, trilostane (Vetoryl) has become a popular drug commonly used for treatment of dogs with hyperadrenocorticism (Cushing’s syndrome) (1,2). Trilostane is a synthetic nonhormonal steroid analog that acts to inhibit the adrenocortical enzyme 3-beta-hydroxysteroid dehydrogenase, as well as 11-beta hydroylase. By blocking these adrenocortical enzymes, trilostane acts to actively interfere with the adrenal’s metabolic pathways and decreases the synthesis of the adrenal end products, including both cortisol and aldosterone (1-3).

Currently, the initial dosage of trilostane recommended by the manufacturer ranges 2.2-6.7 mg/kg, given orally once each day. However, it is clear that the duration of adrenal inhibition in most dogs is much less than 24 hours (1,4,5), and a number of adverse reactions can develop secondary to the drug, especially if higher doses are given (6-12).

Because it is known that trilostane generally has a duration of effect that is less than 24 hours, further investigation of a twice daily dosing regimen is warranted. Dividing the daily dose into twice daily administration might also help lower the prevalence of adverse effects associated with the drug. The purpose of this current study by Feldman (13) was to carefully evaluate the effects of twice-daily, lower-dose trilostane treatment administered to dogs with naturally occurring Cushing’s syndrome.

Objective—To evaluate effectiveness and incidence of adverse reactions to twice-daily lower-dose oral administration of trilostane in the treatment of dogs with naturally occurring hyperadrenocorticism.

Design—Clinical trial.

Animals—47 dogs with naturally occurring hyperadrenocorticism.

Procedures—47 dogs were treated orally with trilostane (0.21 to 1.1 mg/kg, q 12 h). All dogs were reevaluated at 2 weeks and 2 months, 38 dogs at 6 months, and 28 dogs at 1 year of treatment.

Results—9 of 47 dogs had an adrenocortical tumor causing hyperadrenocorticism, and all had good responses after 2 months (mean trilostane dosage, 0.89 mg/kg, q 12 h). All successfully underwent surgical adrenal tumor extirpation.

Thirty-eight dogs had pituitary-dependent hyperadrenocorticism (PDH); 15 dogs did not require a dose increase during the study, and at each of 4 reevaluations, 10 of 15, 13 of 15, 14 of 15, and 11 of 11 had a good response. Twenty-three dogs with PDH had their dose or frequency of trilostane administration increased during the study.

Mean trilostane dosage at 1-year reevaluation in dogs with a good response was 1.7 mg/kg (0.8 mg/lb), twice daily, or 1.1 mg/kg, 3 times daily. At each of 4 reevaluations, 17 of 23, 14 of 23, 17 of 23, and 13 of 17 dogs with PDH had a good response. Five dogs became ill because of trilostane-induced adverse effects, but only 1 required hospitalization.

Conclusions and Clinical Relevance—Administration of initial lower doses of trilostane to dogs with hyperadrenocorticism is effective.

Bottom Line: 

Initial daily dosage of trilostane
When this drug was first used in Europe over a decade ago, the original starting dose was 4-10 mg/kg/day (7-12). However, as experience with the drug grew, it became apparent that these doses were too high in many dogs and lower doses were needed. Accordingly, the dosing recommendation on the US package insert states that an initial daily dose of 2.2-6.7 mg/kg is recommended (4).

My recommended starting dose is either 2 mg/kg given once daily or 1 mg/kg given twice daily. This is similar to the doses used in this study by Feldman (13), where the mean trilostane dose administered to his dogs was 0.86 mg/kg, twice daily (or a mean total daily dose of 1.72 mg/kg). Like Feldman, I feel that it is best to start with a daily dose that is at the low end or even lower than that recommended in the package insert.  I would never start a dog on a dose at the higher end of the recommended dosage range (4-7 mg/kg), although some dogs with Cushing’s disease will eventually require daily doses that may be this high or even higher (1,14).

SID, BID, or TID administration?
Whether to start with once- or twice-daily trilostane administration is controversial (1,2). Although most dogs are controlled clinically with once-daily dosing, trilostane may begin to lose its effectiveness 8-10 hours after administration, so twice daily dosing may be necessary in a subset of dogs (1,4).

In addition, it is very possible that the efficacy of twice-daily dosing might be more effective than once-daily dosing in controlling the complications of Cushing’s syndrome (e.g., proteinuria or hypertension). However, the answer that question remains unclear (15), and additional studies are needed to resolve that issue.

So what do I recommend? Until it is proven that SID or BID treatment is better, I prefer to start with a twice-daily regimen —if feasible and the owner agrees —because controlling cortisol concentrations throughout as much of the day as possible makes sense to me. In diabetic dogs with concurrent Cushing’s disease, twice-daily administration is essential in avoiding large fluctuations in serum cortisol concentrations during the day (1,2). With once-daily trilostane administration, adequate diabetic control will be next to impossible in many dogs with concurrent Cushing's syndrome.

What about TID administration? In this study, 9 (24%) of the 38 dogs with PDH were eventually switched to a regime of trilostane, administered every 8 hours. In my practice, I have not found it necessary to use TID dosing, and I do not find that dose schedule very practical or realistic for most owners.  If I can't remember to "take a pill" every 8 hours (and I can't!), how can we really expect the owners to give their dog a medication three times a day for the rest of their dog's life?

Monitoring & the goals of therapy
We must use a combination of the dog's clinical response and the results of ACTH stimulation testing to monitor dogs on trilostane treatment. In this paper (13), Feldman had three goals of therapy, which included the following:

• a post-ACTH serum cortisol concentration ≤ 5.5 μg/dl (3-4 hours after the morning dose) 
• a urine specific gravity > 1.020 
• owner satisfaction in dog’s improvement.

Of these 3 goals, I agree completely with the last one — the owner's evaluation of the clinical response is key. As far as the urine specific gravity goes, I would agree that most dogs will be able to concentrate their urine to greater than 1.020 once the polyuria resolves. However, if the urine specific gravity is less than 1.020, I would certainly not raise the dose if the owner reported a good clinical response and serum cortisol concentrations were lowered to within the desired range.

Dosage adjustments — raising the dose
In this paper, Feldman recommends that dogs that continue to be symptomatic with a post-ACTH stimulation serum cortisol concentration > 5.5 μg/dl should have the daily dose of trilostane increased. I agree with that recommendation. However, the 5.5 μg/dl cutoff value used in his study was not very sensitive — 40 of the 122 dogs (or a third of cases of this report) with a good clinical response to trilostane had a post-ACTH serum cortisol concentrations higher than 5.5 μg/dl.

For my cases, I recommend maintaining a post-ACTH cortisol concentration between 2-7 μg/dl when tested 4-5 hours after the morning dose. So for a dog that was clinically improved but has a post-ACTH cortisol above 5.5 μg/dl but  below 7.0 μg/dl, I would not recommend increasing the dose in those dogs. Many of those dogs will go on for months on the same dosage, without the need for a higher dose.

Dosage adjustments — lowering the dose
In this report (13), trilostane treatment was continued in dogs with a post-ACTH cortisol concentration less than 1.5 μg/dl, as long as no adverse clinical signs were reported. I disagree with that regime.

When using trilostane, it has become increasing clear that we do not want the cortisol values to drop too low, because that may indicate early or mild adrenal necrosis (1,11,12). In contrast to the protocol used in this reported study, I recommend stopping the drug in all dogs that develop a ACTH-stimulated cortisol values less than 2.0 μg/dl, and repeating the ACTH stimulation test in 1- to 2-weeks in those dogs. Some of these dogs will require that the drug be restarted at a lower dosage, but others will maintain low to normal serum cortisol concentrations for prolonged periods of time. And a subset of these dogs, presumably because of mild adrenal necrosis, will never need any further trilostane treatment to control the signs of Cushing's syndrome.

References:

1. 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.
2. Ramsey IK. Trilostane in dogs. Vet Clin North Am Small Anim Pract 2010;40:269-283. 
3. Wenger M, Sieber-Ruckstuhl NS, Muller C, et al. Effect of trilostane on serum concentrations of aldosterone, cortisol, and potassium in dogs with pituitary-dependent hyperadrenocorticism. Am J Vet Res 2004;65:1245-1250. 
4. Dechra Veterinary Products, U.S. Website. Vetoryl package insert. Overland Park, Kan: Dechra Veterinary Products, 2008.
5. Alenza DP, Arenas C, Lopez ML, et al. Long-term efficacy of trilostane administered twice daily in dogs with pituitary-dependent hyperadrenocorticism. J Am Anim Hosp Assoc 2006;42:269-276. 
6. Vaughan MA, Feldman EC, Hoar BR, et al. Evaluation of twice-daily, low-dose trilostane treatment administered orally in dogs with naturally occurring hyperadrenocorticism. J Am Vet Med Assoc 2008;232:1321-1328. 
7. Neiger R, Ramsey I, O'Connor J, et al. Trilostane treatment of 78 dogs with pituitary-dependent hyperadrenocorticism. Vet Rec 2002;150:799-804. 
8. Ruckstuhl NS, Nett CS, Reusch CE. Results of clinical examinations, laboratory tests, and ultrasonography in dogs with pituitary-dependent hyperadrenocorticism treated with trilostane. Am J Vet Res 2002;63:506-512.
9. Braddock JA, Church DB, Robertson ID, et al. Trilostane treatment in dogs with pituitary-dependent hyperadrenocorticism. Aust Vet J 2003;81:600-607. 
10. Bell R, Neiger R, McGrotty Y, et al. Study of the effects of once daily doses of trilostane on cortisol concentrations and responsiveness to adrenocorticotrophic hormone in hyperadrenocorticoid dogs. Vet Rec 2006;159:277-281. 
11. Chapman PS, Kelly DF, Archer J, et al. Adrenal necrosis in a dog receiving trilostane for the treatment of hyperadrenocorticism. J Small Anim Pract 2004;45:307-310. 
12. Ramsey IK, Richardson J, Lenard Z, et al. Persistent isolated hypocortisolism following brief treatment with trilostane. Aust Vet J 2008;86:491-495. 
13. Feldman EC. Evaluation of twice-daily lower-dose trilostane treatment administered orally in dogs with naturally occurring hyperadrenocorticism. J Am Vet Med Assoc 2011;238:1441-1451. 
14. Feldman EC, Kass PH. Trilostane dose versus body weight in the treatment of naturally occurring pituitary-dependent hyperadrenocorticism in dogs. J Vet Intern Med 2012;26:1078-1080. 
15. Smets PM, Lefebvre HP, Meij BP, et al. Long-term follow-up of renal function in dogs after treatment for ACTH-dependent hyperadrenocorticism. J Vet Intern Med 2012;26:565-574. 

Top Endocrine Publications of 2011: The Canine Adrenal Gland

In my seventh compilation of the canine and feline endocrine publications of 2011, I’m moving on to disorders of the canine adrenal gland.

Listed below are 35 research papers written in 2011 that deal with a variety of adrenal gland issues of clinical importance in dogs.

These range from the investigations of typical (13,27), atypical (24,28), or pseudo-hypoadrenocorticism (32) to a case report of hyporeninemic hypoaldosteronism (16); from diagnostic testing for Cushing's syndrome (5,10,11,34) to imaging studies for evaluation and differentiation of adrenal disease (4,23,25); from studies of the relationship between gallbladder mucoceles and glucocorticoid excess (15,21) to and to dermatologic aspects of Cushing's disease (35).

Other research studies investigated the use of trilostane (3,8,12,20) to an overview of adrenalectomy for dogs with adrenal gland tumors (17,19); from complications associated with transsphenoidal surgery (31) to the effect of lignans and melatonin treatment on adrenocortical secretion (7); and finally, the report of an experimental new medical approach to treating Cushing's disease using a tyrosine kinase inhibitor to block epidermal growth factor receptor located on the pituitary adenoma, which inhibited corticotroph tumor cell proliferation and induced apotosis (9,33).

Other studies include the investigation of a radionuclide therapy for canine pheochromocytoma (2) to a case report of pheochromocytoma diagnosed by use of magnetic resonance imaging (29).

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. Bommarito DA, Lattimer JC, Selting KA, et al. Treatment of a malignant pheochromocytoma in a dog using 131I metaiodobenzylguanidine. J Am Anim Hosp Assoc 2011;47:e188-194. 
3. Burkhardt WA, Guscetti F, Boretti FS, et al. Adrenocorticotropic hormone, but not trilostane, causes severe adrenal hemorrhage, vacuolization, and apoptosis in rats. Domest Anim Endocrinol 2011;40:155-164. 
4. Choi J, Kim H, Yoon J. Ultrasonographic adrenal gland measurements in clinically normal small breed dogs and comparison with pituitary-dependent hyperadrenocorticism. J Vet Med Sci 2011;73:985-989. 
5. Cisneros LE, Palumbo MI, Mortari AC, et al. What is your neurologic diagnosis? Hyperadrenocorticism. J Am Vet Med Assoc 2011;238:1247-1249. 
6. de Brito Galvao JF, Chew DJ. Metabolic complications of endocrine surgery in companion animals. Vet Clin North Am Small Anim Pract 2011;41:847-868. 
7. Fecteau KA, Eiler H, Oliver JW. Effect of combined lignan phytoestrogen and melatonin treatment on secretion of steroid hormones by adrenal carcinoma cells. Am J Vet Res 2011;72:675-680. 
8. Feldman EC. Evaluation of twice-daily lower-dose trilostane treatment administered orally in dogs with naturally occurring hyperadrenocorticism. J Am Vet Med Assoc 2011;238:1441-1451. 
9. Fukuoka H, Cooper O, Ben-Shlomo A, et al. EGFR as a therapeutic target for human, canine, and mouse ACTH-secreting pituitary adenomas. J Clin Invest 2011;121:4712-4721. 
10. Gilor C, Graves TK. Interpretation of laboratory tests for canine Cushing's syndrome. Top Companion Anim Med 2011;26:98-108. 
11. Graves TK. When normal is abnormal: keys to laboratory diagnosis of hidden endocrine disease. Top Companion Anim Med 2011;26:45-51. 
12. Helm JR, McLauchlan G, Boden LA, et al. A comparison of factors that influence survival in dogs with adrenal-dependent hyperadrenocorticism treated with mitotane or trilostane. J Vet Intern Med 2011;25:251-260. 
13. Hughes AM, Bannasch DL, Kellett K, et al. Examination of candidate genes for hypoadrenocorticism in Nova Scotia Duck Tolling Retrievers. Vet J 2011;187:212-216. 
14. Klose TC, Creevy KE, Brainard BM. Evaluation of coagulation status in dogs with naturally occurring canine hyperadrenocorticism. J Vet Emerg Crit Care (San Antonio) 2011;21:625-632. 
15. Kook PH, Schellenberg S, Rentsch KM, et al. Effect of twice-daily oral administration of hydrocortisone on the bile acids composition of gallbladder bile in dogs. Am J Vet Res 2011;72:1607-1612. 
16. Kreissler JJ, Langston CE. A case of hyporeninemic hypoaldosteronism in the dog. J Vet Intern Med 2011;25:944-948. 
17. Lang JM, Schertel E, Kennedy S, et al. Elective and emergency surgical management of adrenal gland tumors: 60 cases (1999-2006). J Am Anim Hosp Assoc 2011;47:428-435. 
18. Martin LG. Critical illness-related corticosteroid insufficiency in small animals. Vet Clin North Am Small Anim Pract 2011;41:767-782.
19. Massari F, Nicoli S, Romanelli G, et al. Adrenalectomy in dogs with adrenal gland tumors: 52 cases (2002-2008). J Am Vet Med Assoc 2011;239:216-221. 
20. McGraw AL, Whitley EM, Lee HP, et al. Determination of the concentrations of trilostane and ketotrilostane that inhibit ex vivo canine adrenal gland synthesis of cortisol, corticosterone, and aldosterone. Am J Vet Res 2011;72:661-665. 
21. Norwich A. Gallbladder mucocele in a 12-year-old cocker spaniel. Can Vet J 2011;52:319-321. 
22. Notari L, Mills D. Possible behavioral effects of exogenous corticosteroids on dog behavior: a preliminary investigation. J Vet Behavior 2011;6:321-327. 
23. Pey P, Vignoli M, Haers H, et al. Contrast-enhanced ultrasonography of the normal canine adrenal gland. Vet Radiol Ultrasound 2011;52:560-567. 
24. Richartz J, Neiger R. Hypoadrenocorticism without classic electrolyte abnormalities in seven dogs. Tierarztl Prax Ausg K Kleintiere Heimtiere 2011;39:163-169. 
25. Rodriguez Pineiro MI, de Fornel-Thibaud P, Benchekroun G, et al. Use of computed tomography adrenal gland measurement for differentiating ACTH dependence from ACTH independence in 64 dogs with hyperadenocorticism. J Vet Intern Med 2011;25:1066-1074. 
26. Ryan VH, Trayhurn P, Hunter L, et al. 11-Hydroxy-beta-steroid dehydrogenase gene expression in canine adipose tissue and adipocytes: stimulation by lipopolysaccharide and tumor necrosis factor alpha. Domest Anim Endocrinol 2011;41:150-161. 
27. Seth M, Drobatz KJ, Church DB, et al. White blood cell count and the sodium to potassium ratio to screen for hypoadrenocorticism in dogs. J Vet Intern Med 2011;25:1351-1356. 
28. Snead E, Vargo C, Myers S. Glucocorticoid-dependent hypoadrenocorticism with thrombocytopenia and neutropenia mimicking sepsis in a Labrador retriever dog. Can Vet J 2011;52:1129-1134. 
29. Spall B, Chen AV, Tucker RL, et al. Imaging diagnosis-metastatic adrenal pheochromocytoma in a dog. Vet Radiol Ultrasound 2011;52:534-537. 
30. Taoda T, Hara Y, Masuda H, et al. Magnetic resonance imaging assessment of pituitary posterior lobe displacement in dogs with pituitary-dependent hyperadrenocorticism. J Vet Med Sci 2011;73:725-731. 
31. Teshima T, Hara Y, Taoda T, et al. Central diabetes insipidus after transsphenoidal surgery in dogs with Cushing's disease. J Vet Med Sci 2011;73:33-39. 
32. Venco L, Valenti V, Genchi M, et al. A dog with pseudo-Addison disease associated with trichuris vulpis Infection. J Parasitol Res 2011;2011:682039. 
33. Wondisford FE. A new medical therapy for Cushing disease? J Clin Invest 2011;121:4621-4623. 
34. Zeugswetter F, Pagitz M, Hittmair K, et al. Diagnostic efficacy of plasma ACTH-measurement by a chemiluminometric assay in canine hyperadrenocorticism. Schweiz Arch Tierheilkd 2011;153:111-116. 
35. Zur G, White SD. Hyperadrenocorticism in 10 dogs with skin lesions as the only presenting clinical signs. J Am Anim Hosp Assoc 2011;47:419-427. 

How Glucocorticoids Affect the Complete Blood Count

What are the effects of glucocorticoids on the results of a hemogram (complete blood count)?

I know that glucocorticoids may cause a neutrophilia. But my main question is —if a dog or cat is on prednisone or another glucocorticoid, how would one know that a neutrophilia was due to a glucocorticoid effect vs. an infectious agent? I've read that if there is no left shift, toxic changes or clinical signs of fever that one could assume it was due to the glucocorticoids. But, is there a number cut-off at which it is too high to be attributable to glucocorticoid administration?

I also remember that glucocorticoids lower lymphocyte numbers (hence it is used to treat leukemia potentially). But what is the mechanism by which it does that?

And finally, what effect do glucocorticoids have on platelet number? How about the effects on red blood cell (RBC) count and hematocrit?

My Response:

Stress leukogram of glucocorticoid excess
The hematological response to glucocorticoid effect is a bit variable between species, but the classic glucocorticoid response in dogs is a mature neutrophilia (without a left shift), lymphopenia, eosinopenia and monocytosis (1-4). In cats, we would more likely see just a neutrophilia with lymphopenia and eosinopenia (without the monocytosis).

This hemogram response associated with glucocorticoid excess is sometimes referred to as a "stress leukogram," since it is also a common and nonspecific finding in many sick or stressed dogs (1).

The major acute effect of steroids on WBCs is to cause "washout" of marginated neutrophils and monocytes from periphery into circulation. Decreased amounts of lymphocytes (peripheral) and eosinophils are seen as glucocorticoids can sequester these cells into the lungs and spleen and prompt decreased release from the bone marrow. When administered chronically at high enough doses, glucocorticoids can cause involution of lymphoid tissue (1,2).

Steroid effect versus a response to infection?
Infectious responses will often be associated with toxic change in the neutrophils or a significant left shift, which is unusual with steroids. The magnitude of the neutrophilia is also helpful to distinguish between a steroid effect and a response to infection. With glucocorticoids, we can see up to 2-fold increase in dogs and up to 3-fold increase in cats (they have different proportions of neutrophils in circulating versus marginated pools). If the magnitude of the patient's neutrophilia is more severe, then infection is more likely.

Increased platelet numbers
Finally, glucocorticoids inhibit platelet aggregation and can also increase platelet numbers.

Erythrocytosis
With chronic administration (or spontaneous Cushing's syndrome), glucocorticoid excess can increase red cell production and diminish removal of old RBCs, resulting in mild erythocytosis.

References:

1. Feldman BF, Zinkl JG, Jain NC (eds): Schalm's Veterinary Hematology (Fifth edition). New York, Wiley-Blackwell, New York, 2000.
2. Behrend EN, Kemppainen RJ. Glucocorticoid therapy. Pharmacology, indications, and complications. Veterinary Clinics of North America: Small Animal Practice 1997;27:187-213. 
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. 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: Adjusting the Trilostane Dose in Dogs with Cushing's Syndrome: Blunted Cortisol Response to ACTH Stimulation

I am using trilostane (Vetoryl, Dechra Animal Health) to treat a 14-year old, MC Poodle (10 kg) with pituitary-dependent Cushing's disease.  He has also been diabetic for the past year. 

Prior to diagnosis of the Cushing's disease and treatment with Vetoryl (10 mg, BID), his diabetes was difficult to control and he was slightly insulin resistant. Now that he is on treatment for the Cushing's disease, his diabetes is well controlled with NPH insulin (7 U, BID). 

It is now 3 months since we started this dog on Vetoryl.  His 30-day recheck was good, with a basal cortisol of 2.0 μg/dl and a post-ACTH cortisol of 5.2 μg/dl. 

On his 90-day recheck, the dog looks great and the result of his CBC, serum chemistry panel and complete urinalysis look good. Results of the ACTH stimulation test, started 4 hours after the morning dose of Vetoryl, revealed a basal cortisol of 3.8 μg/dl, with a post-ACTH value of 4.0 μg/dl. 

I am concerned about the blunted cortisol response to the ACTH injection, more than the absolute numbers. What do you think? Should I lower the dose of the Vetoryl?

My Response

Do not worry about this dog's blunted serum cortisol response— this is a perfect response for a dog on Vetoryl.

As long as both the basal and ACTH-stimulated cortisol concentrations are above 2 μg/dl and the dog is doing well clinically, you should not be concerned about the lack of cortisol response to ACTH stimulation (1,2). In fact, even if the post-ACTH cortisol concentration was lower than the basal cortisol (but both were greater than 2.0 μg/dl), I would still not be concerned.

If all continues to be well, I'd follow-up with another recheck in 3 months. At each recheck, I would recommend at least a serum chemistry panel, urinalysis, and cortisol determinations (1,2). If no signs of relapse are apparent, you might want to monitor only a basal cortisol concentration (3), but I would recommend that you perform an ACTH stimulation test at every other recheck visit at the minimum.

Remember that dogs with either Cushing's disease or diabetes are predisposed to developing urinary tract infections (1), so I also recommend doing a urine culture every 6 months on these dogs with concurrent diabetes and Cushing's syndrome. These dogs can have asymptomatic urinary tract infections, so the urine culture should be done even if they do not show any overt clinical signs of hematuria or stranguria.

References:

1. 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; pp. 1816-1840.
2. Ramsey IK. Trilostane in dogs. The Veterinary Clinics of North America Small Animal Practice 2010;40:269-283.
3. Cook AK, Bond KG. Evaluation of the use of baseline cortisol concentration as a monitoring tool for dogs receiving trilostane as a treatment for hyperadrenocorticism. Jornal of the American Veterinary Medical Association 2010;237:801-805.

Q & A: Managing Dogs with Cushing's Syndrome: Mitotane vs Trilostane?

I had attended your endocrine lectures at the annual meeting of the Minnesota Veterinary Medical Association last month and heard your great talk on how you workup and treat dogs with Cushing's syndrome.

My patient is a 9-year old, FS, Brittany Spaniel, weighing about 20 kg. She has a 6-month history of increased drinking, urination, hunger, and weight gain. 

On her routine blood tests, she had high serum alanine aminotransferase activity (ALT, 152 U/L; reference range, 12-118 U/L), high serum alkaline phosphatase activity (1998 U/L; reference range, 23-212 U/L). The serum cholesterol was also elevated  at 459 mg/dl (reference range, 110-320 mg/dl). I did a serum bile acids test, which was normal.

After I heard your lecture, I did a low-dose dexamethasone suppression test, with the following cortisol results. 

• Cortisol basal sample: 3.3 μg/dl (reference range, 1-5 μg/dl)
• Cortisol 4 hr: 2.2 μg/dl (reference range, 0.0-1.4 μg/dl)
• Cortisol 8 hr: 3.5 μg/dl (reference range, 0.0-1.4 μg/dl)

I know that the lack of cortisol suppression is diagnostic for Cushing's syndrome but the results do not differentiate between pituitary-dependent hyperadrenocorticism and functional adrenal tumor.

The owner is interested in doing an abdominal ultrasound and wants to pursue treatment eventually. So we are planning to set up an appointment for an ultrasound as the next step, but I did have some questions in terms of longer-term outcome for dogs with Cushing's disease. With some of our other suspected cases, the owners have not pursued pituitary-adrenal function testing or treatment due to cost, so I haven't actually had any that I've gone on to treat (I've also only been practicing since July 2010).  

1. If it is an adrenal tumor, you had recommend treating with trilostane for several weeks prior to surgical adrenalectomy, correct? Does this help to minimize post-operative complications?
2. And if they go on to surgery, and it comes back as benign, do most dogs do pretty well after long-term?
3. If the owner cannot afford/does not want to pursue surgery, can they do relatively well on trilostane (provided it isn't a carcinoma)?
4. If pituitary-dependent and treated with trilostane, do dogs do pretty well long-term? I wasn't sure about their long-term prognosis.

Thanks for you time in advance. I really appreciate any insight you're able to give me since again, we haven't really treated many dogs at my clinic.

My Response:

In answer to your questions:

1. Yes, if this dog has an adrenal tumor, I recommend treating with trilostane (Vetoryl, Dechra Animal Health) for 4-6 weeks prior to surgery (1,2). Controlling the high cortisol values prior to surgery helps to minimize post-operative complications, such as thromboembolism, poor wound healing, and infections.
2. If the dog has a benign adrenal tumor which is removed surgically, the dog would be cured (1). Post-operatively, she will go through a period of adrenal insufficiency (remember that the contralateral adrenal cortex is suppressed and will take a few weeks to start working again). During the immediate post-operative period, glucocorticoid supplementation should be initiated. The doses of the daily glucocorticoids should then be slowly tapered over the next 6-8 weeks, when they can generally be discontinued in most dogs.
3. If the owner cannot afford the cost of adrenalectomy or does not want to pursue surgery, most dogs can be controlled relatively well on trilostane (Vetoryl) but will never be cured (1-3). Overall, the prognosis with medical treatment is not as good as surgical treatment. If the dog has adrenal carcinoma, medical treatment will not prevent tumor growth, invasion into the vena cava, or metastasis (1).
4. If the dog has pituitary-dependent hyperadrenocorticism (PDH) and is treated with trilostane (Vetoryl), most dogs do well when treated with either mitotane (Lysodren) or trilostane. Studies have reported that there is no difference in survival between use of either of these drugs (4,5).

Botton line— We need a differentiating test to help guide our treatment recommendations and determine prognosis. Let me know when you have the results of the abdominal ultrasound on this dog.

Follow-up:

The abdominal ultrasound was just done this morning. Both adrenals were at the upper end of normal size —not nodular— and no masses found on either adrenal gland. 

So these imaging results are consistent with pituitary-dependent Cushing's disease, correct?

My Response:

Yes, your dog has PDH and can be treated with either trilostane or mitotane.

Remember to explain to the owner, however, the dog's problem lies in the pituitary gland, not the adrenal glands. Most of these dogs will have small pituitary tumors that tend to grow slowly over time (1,6,7). Others, however, have large pituitary tumors at time of diagnosis and some of these tumors expand more rapidly and can cause compression of the hypothalamus and lead to neurological signs.

Hopefully, your patient will be well-controlled with the medical treatment and will die of old age before the development of a large, invasive pituitary tumor becomes and issue.

References:

1. 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; pp. 1816-1840.
2. Ramsey IK. Trilostane in dogs. The Veterinary Clinics of North America Small Animal Practice 2010;40:269-283. 
3. Helm JR, McLauchlan G, Boden LA, et al. A comparison of factors that influence survival in dogs with adrenal-dependent hyperadrenocorticism treated with mitotane or trilostane. Journal of Veterinary Internal Medicine 2011; 25:251-260.  
4. Clemente M, De Andrés PJ, Arenas C, et al. Comparison of non-selective adrenocorticolysis with mitotane or trilostane for the treatment of dogs with pituitary-dependent hyperadrenocorticism. Veterinary Record 2007;161:805-809.
5. Kintzer PP, Peterson ME. Mitotane (o,p'-DDD) treatment of 200 dogs with pituitary-dependent hyperadrenocorticism. Journal of Veterinary Internal Medicine  1991;5:182-90. 
6. Ihle SL. Pituitary corticotroph macrotumors. Diagnosis and treatment. The Veterinary Clinics of North America Small Animal Practice 1997;27:287-297. 
7. Kent MS, Bommarito D, Feldman E, et al. Survival, neurologic response, and prognostic factors in dogs with pituitary masses treated with radiation therapy and untreated dogs. Journal of Veterinary Internal Medicine 2007;21:1027-1033. 

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.

Q & A: Addison's Disease in a Cat with Juvenile Diabetes

I have a 2-year old, male-neutered DSH cat who had had diabetes mellitus since 4 months of age. He has been very difficult to regulate, but his diabetic regulation and glucose control is much better since changing to ProZinc^®  insulin (Boehringer Ingelheim).

In the past, he has developed recurrent episodes of diabetic ketoacidosis. During each of these episodes, the cat had hyponatremia and hypochloremia. Because of these serum electrolyte changes and the fact that we are having trouble getting him to gain weight, I thought that Addison's disease should be ruled out.

I ran a baseline cortisol concentration 1 week ago, and the value was low at 0.7 μg/dl (reference range, 1.0-4.0 μg/dl). I did an ACTH stimulation test this week to rule out Addison's disease. For this test, I used cosyntropin (Cortrosyn^®) and administered a whole vial (0.25 mg or 250 μg), IV. The results of cortisol results before and after ACTH administration are as follows:

• 0 min (Pre-ACTH): 2.4 μg/dl (reference range, 1.0-4.0 μg/dl)
• 30 min (Post-ACTH): 5.3 μg/dl (reference range, 5.0-12.5 μg/dl)
• 60 min (Post-ACTH): 4.4 μg/dl (reference range, 5.0-12.5 μg/dl)

As you can see, the basal cortisol value is now completely within normal range, but both ACTH-stimulated cortisol values are low-normal. I don't understand why the baseline cortisol was so low 2 weeks ago but now it's so normal. But the response to ACTH stimulation still appears blunted.

Did I do the test correctly? Does this cat have Addison's disease or not?

My Response:

Both cortisol and ACTH are secreted in pulses throughout the day (episodic secretion) with peaks and valleys in hormone levels (1). So it would be very possible to take two serum samples for cortisol measurement just separated by just a few minutes and obtain two very different cortisol values. In my experience, cats tend to have lower basal cortisol concentrations than dogs, so the value of 0.7 μg/dl may be "normal," at least for this cat.

As far as this cat's blunted cortisol response to the cosyntropin (Cortrosyn^®)  injection, cats do not always respond as well as dogs (2,3), so I would consider this cat's ACTH stimulation test to be normal. Again, the post-ACTH peak serum cortisol concentrations tend to be lower in normal cats than the cortisol response seen in dogs. Because an low-normal cortisol response in a cat could be interpreted as severely blunted if the canine reference range is used, it is important for each laboratory to establish their own reference range values for cats. Obviously not all labs have actually done the work necessary to properly establish their own reference range values for all hormones, especially in the cat.

The bottom line: These results completely rule out Addison's disease.

Your protocol for performing the ACTH stimulation test in this cat is fine and certainly provided maximal adrenocortical stimulation, which is the goal of the ACTH stimulation test. Cosyntropin is the preferred ACTH preparation in cats, as it is in dogs. But let's talk more the best protocol for performing this test in cats, because there are some major differences between ACTH test protocols in cats and dogs.

First of all, the route of administration is very important in cats. In dogs, cosyntropin can be administered either IV or IM, with an equivalent cortisol response. In contrast, Cortrosyn should be administered IV to cats, because the adrenocortical response is more consistent and the peak cortisol is higher when given by that route. Given intramuscularly, the cosyntropin is not well absorbed in cats. In addition, giving cosyntropin by the IM route is painful for cats and therefore should be avoided.

Traditionally, it has been recommended that we collect post-ACTH cortisol samples at 30 and 60 minutes in cats to ensure detection of the peak cortisol response (4). However, this was based on the use of the intramuscular route of administration, where the peak cortisol response is lower and occurs earlier, generally at 30 minutes (4). By using the IV route of administration, the peak cortisol response in cats, as well as dogs, occur by 60 to 75 minutes after injection, so a sampling time of 60 minutes is recommended (2,3,5).

For many years, we have recommended administration of a relatively large dose of cosyntropin (125 μg per cat) to ensure an adequate and prolonged adrenocortical response in cats. However, it is clear that this 125-µg dose of cosyntropin, at least when administered IV, exceeds that needed to induce maximal adrenocortical stimulation in clinically normal cats, and that smaller doses can maximally stimulate the adrenal cortex (3,5).

A recent report evaluated the lowest feline dose of cosyntropin, based on body weight, that produced maximal cortisol secretion equivalent to that achieved with the standard dose of 125 μg per cat (5). In that study, the lowest cosyntropin dose that resulted in maximal cortisol response was 5 μg/kg and occurred at 60 to 75 minutes after IV cosyntropin administration. This 5 μg/kg cosyntropin dose is identical to that generally used in dogs for ACTH stimulation testing.

The bottom line: Low-dose ACTH stimulation testing with 5 μg/kg cosyntropin given IV followed by blood sample collection at 60 minutes in cats produced results equivalent to those produced by the traditional 125 μg per cat dose.

Lastly, let me comment about this cat's diabetes. Juvenile diabetes is extremely rare in cats (6,7). Most of these cats appear to have hypoplasia of the pancreatic islets, so almost all are life-long diabetics. Typically, cats and dogs with juvenile diabetes mellitus are extremely brittle, prone to ketoacidosis, and difficult to regulate. Therefore, I'm very pleased to learn that this diabetic cat is doing so well on the twice daily ProZinc insulin.

References:

1. Kemppainen RJ, Peterson ME. Domestic cats show episodic variation in plasma concentrations of adrenocorticotropin, alpha-melanocyte-stimulating hormone (alpha-MSH), cortisol and thyroxine with circadian variation in plasma alpha-MSH concentrations. European Journal of Endocrinology 1996;134:602-609.
2. Peterson ME, Kemppainen RJ: Comparison of intravenous and intramuscular routes of administering cosyntropin for corticotropin stimulation testing in cats. American Journal of Veterinary Research 53:1392-1395, 1992.
3. Peterson ME, Kemppainen RJ: Dose-response relation between plasma concentrations of corticotropin and cortisol after administration of incremental doses of cosyntropin for corticotropin stimulation testing in cats. American Journal of Veterinary Research 54:300-304, 1993.
4. Smith MC, Feldman EC. Plasma endogenous ACTH concentrations and plasma cortisol responses to synthetic ACTH and dexamethasone sodium phosphate in healthy cats. American Journal of Veterinary Research 1987;48:1719-1724.
5. DeClue AE, Martin LG, Behrend EN, et al. Cortisol and aldosterone response to various doses of cosyntropin in healthy cats. Journal of the American Veterinary Medical Association 2011;238:176-182.
6. Woods PJ, Panciera DL, Snyder PS, et al. Diabetes mellitus in a kitten. Journal of the American Animal Hospital Association 1994; 30:177-180.
7. Thoresen SI, Bjerkås E, Aleksandersen M, et al. Diabetes mellitus and bilateral cataracts in a kitten. Journal of Feline Medicine and Surgery 2002; 4:115-22.

To see more of my related posts on this topic, click on the links below:

• What ACTH Preparations Should Be Used For Stimulation Testing? 

• What's the Best Protocol for ACTH Stimulation Testing in Dogs and Cats?

Q & A: How is the Urinary Cortisol Creatinine Ratio Calculated?

This patient is a 5.5-year-old male neutered Westie that presents with the main complaints of polyuria and polydipsia (PU/PD). The results of a CBC and serum chemistry panal were normal. Strangely, however, the dog has glucosuria with no hyperglycemia. We have run multiple samples on different days of both blood and urine, all showing positive glucosuria but normoglycemia.

I submitted a urine cortisol:creatinine ratio (UCCR)to screen for Cushing's syndrome. It was not the ideal, home-caught, first in AM urine sample. It was free catch urine sample collected here at the clinic. Results show a UCCR ratio of 115. But the urine cortisol is 8.5 μg/dl (normal for Idexx laboratories reference range) and the creatinine is 23.1 mg/dl (low for the reference range). So, am I correct to interpret that the ratio is high because the creatinine is low and not because the cortisol is high? Can Cushing's syndrome be ruled out, or should I proceed to further Cushing's diagnostics?

My Response:

We do the UCC-ratio to correct for increased/decreased filtration and we therefore ought to look at the ratio, not the individual results. Therefore we cannot rule out Cushing's syndrome based on this result. You could, however, repeat measurements on a few home collected, morning samples. It is interesting that the serum alkaline phosphatase is normal in this, which, although still possible, makes hyperdrenocorticism less likely. It still is an important differential though. You could also run a fructosamine to check for chronic relative hyperglycemia.

Q & A: How Does Human Addison's Compare to the Canine Disease?

I don't know if I should even ask this but a situation in my family has me curious. My sister-in-law was diagnosed with pituitary-dependant Addison's disease over five years ago. She has been treated since that time with florinef and prednisone and has been doing well. Recently she had a recheck and an ACTH stimulation test while on treatment and she had a resting cortisol around 10 µg/dl and post around 20 µg/dl. 

Now she's being weaned off of treatment and told her pituitary and adrenals are fine. I've never done an ACTH stimulation test on an animal I'm treating for Addison's disease after it's diagnosed and was wondering about the rational for doing that. Is human Addison's disease curable? Is there something completely different in human Addison's from the canine disease, or am I just missing something? 

If anyone has an opinion and would like to share I'd appreciate it. Curiosity is getting the best of me. 
Thank you.

My Response:

It sounds to me as if they didn't believe the diagnosis of Addison's disease so they repeated the ACTH stimulation test. Addison's disease doesn't resolve once it develops (in either dogs or humans), and there is no such thing as "pituitary-dependent" Addison's disease.

On a brighter note, its's great news that your sister-in-law is normal!

Couldn't you theoretically get glucocorticoid deficiency from lack of production of ACTH? (Kind of like a central diabetes insipidus dog having a central lesion?)

My Response:

Absolutely. But pituitary ACTH deficiency is "secondary" hypoadrenocorticism, not Addison's disease.

Sorry to be such a stickler about terminology, but when Sir Thomas Addison described the disease that now uses his name, all of the patients had "primary" hypoadrenocorticism with complete destruction of both adrenal cortices.Therefore, the term Addison disease should be restricted to those patients with the primary form of the disorder (ie, those that have both glucocorticoid and mineralocorticoid deficiency).

There is no such disease as pituitary Addison's disease. Why? Because, like we all know, pituitary ACTH deficiency can not cause destruction of the adrenal gland or lead to mineralocorticoid deficiency. ACTH deficiency would only cause cortisol deficiency.

When we use the term Addison's so loosely, it becomes very confusing. It really would be best to avoid the use of the term completely. But we know that will never happen!

Adrenal Tumors in Cats

Click here to view the slides as you read through this lecture.

Adrenal tumors are an uncommon finding in cats. Based on available data, it is estimated that approximately 0.03% of the feline population (representing 0.2% of all cat tumors) develop a primary adrenal gland tumour. Metastasis to the adrenal glands from other organs is uncommon but when it does occur, lymphoma seems to be the most common (1).

An adrenal tumour may be functional (i.e., producing and secreting a hormone) or nonfunctional. In cats, adrenocortical tumors can secrete excessive amounts of cortisol, progesterone and other sex steroid hormones, or aldosterone. Feline adrenal medullary tumors (pheochromocytoma), although extremely rare, secrete excessive amounts of catecholamines.

Cortisol-Secreting Adrenal Tumors
A cortisol-secreting adrenal mass causing hyperadrenocorticism is the most common functional adrenal tumour identified in cats. Naturally occurring hyperadrenocorticism (Cushing’s syndrome) is rare in cats (2-4). Pituitary-dependent hyperadrenocorticism accounts for the majority of cases, but cortisol-secreting adrenocortical neoplasia is responsible in approximately 20% of cats. About one-third of theses adrenal tumors in cats are malignant.

Historical and clinical findings in cats with cortisol-secreting adrenal tumors may include lethargy, weakness, pendulous abdomen, thin fragile skin, bilaterally symmetric alopecia, dull haircoat, seborrhea sicca, muscle atrophy, polyuria, polydipsia, and polyphagia (2-4). In contrast to dogs with hyperadrenocorticism, polyuria and polydipsia in affected cats appear to be secondary to concurrent diabetes mellitus in the vast majority of cases. Hyperglycemia and glycosuria are seen in up to 90% of cats and hypercholesterolemia and elevated serum ALT activity are common. However, a high serum alkaline phosphatase activity is not a consistent finding in cats with hyperadrenocorticism.

In addition to the typical clinical signs and clinicopathologic findings associated with hyperadrenocorticism, diagnosis of hyperadrenocorticism due to a functional adrenal tumour is confirmed using tests of pituitary-adrenocortical axis (ie, high dose dexamethasone suppression test and endogenous ACTH concentrations). Finally, imaging studies (ie, abdominal ultrasound, CT, MR) should be used to confirm the presence of an adrenal tumour in these cats (2-4). In cats with adrenal-dependent hyperadrenocorticism, the contralateral adrenal gland is expected to be small or atrophied as a result of suppressed pituitary ACTH secretion.

Unilateral adrenalectomy is most successful method of treating cats with cortisol-secreting adrenocortical tumour (2-5). In cats with adrenal adenoma or adrenal carcinoma that has not yet metastasized, adrenalectomy may be curative. If tumour resection is successful, circulating cortisol fall to low concentrations and these cats generally require glucocorticoid supplementation for approximately two months postoperatively until the glucocorticoid secretory function of the atrophied contralateral gland recovers.

Because of the deleterious effects of chronic cortisol excess on skin fragility as well as on immune and cardiovascular function, many cats with untreated hyperadrenocorticism are poor surgical candidates. Surgery has been difficult to perform owing to the debilitated condition of these cats. Although further investigation needs to be done, trilostane (5-15 mg/kg) appears to be useful in the preoperative preparation of these cats prior to adrenalectomy (3,6). In those cats that are not surgical candidate or have adrenal tumour metastasis, trilostane (Vetoryl. Dechra Veterinary Products) may also be useful in their long-term management, at least for a few weeks to months.

Sex hormone Secreting Adrenal Tumors
A functional tumour arising from the adrenal cortex could secrete excessive amounts of adrenal progestagens, androgens, or estrogens. Progesterone-secreting adrenal tumors have been the most common sex hormone secreting adrenal tumour reported in cats (6-10). Clinical signs are similar to those in cats with cortisol-secreting tumors. Excessive progesterone secretion in affected cats causes diabetes mellitus and feline fragile skin syndrome, which is characterized by progressively worsening dermal and epidermal atrophy, endocrine alopecia, and easily torn skin. In most of these cats with progesterone-secreting adrenal tumors, results of tests of the pituitary-adrenocortical axis are normal to suppressed and the contralateral adrenal gland is normal in size and shape on abdominal ultrasound. Diagnosis requires documenting an increased concentration of one or more adrenal sex steroids, ideally measured before and after ACTH stimulation.
Recently, a male cat that had developed strong urine order and aggressive behaviour was documented to have a functional adrenal adenoma associated with high circulating concentration of androstenedione and testosterone (11). After adrenalectomy, serum concentrations of the androgens decreased and urine spraying urine aggression resolved.

Aldosterone Secreting Adrenal Tumors
Primary hyperaldosteronism (Conn's syndrome) appears to be a relatively rare but greatly underdiagnosed disease of older cats. This syndrome is characterized by excessive autonomous secretion of aldosterone from one or both adrenal glands, resulting in clinical signs relating to hypertension and/or hypokalemia (13-16).

About half of cases have been due to unilateral aldosterone-secreting adrenal adenomas, whereas most of the remaining cats have unilateral adrenal carcinomas. Less commonly, bilateral adrenal adenomas or bilateral adrenal hyperplasia (17) have been reported. Occasionally, an aldosterone-secreting adrenal tumour is also found to be hypersecreting another adrenocortical hormone, most commonly progesterone (9,11); these cats also had diabetes mellitus and dermatologic changes, both attributed to progesterone excess rather than hyperaldosteronism.
Aldosterone is the major mineralocorticoid secreted by the adrenal cortex and is responsible for regulation of sodium and potassium balance. Therefore, the hormone helps maintain intravascular fluid volume and acid-base balance. Historical findings are generally nonspecific can include generalized weakness (sometimes episodic), lethargy, stiffness, muscle pain, polyuria/polydipsia, and blindness (13-17). Physical examination findings might include ventroflexion of the neck, hypertension, blindness, and retinal vessel tortuosity.

Cats with hyperaldosteronism commonly have moderate to severe hypokalemia and metabolic alkalosis. The sodium concentration is normal to mildly elevated. Demonstration of an inappropriately elevated serum aldosterone concentration along with a low plasma renin concentration provides a definitive diagnosis of hyperaldosteronism. Ideally a diagnosis is made on the basis of marked hyperaldosteronemia in conjunction with hypertension, hypokalemia, inappropriate kaliuresis (high urinary fractional excretion of potassium), and low plasma renin activity (14-17). The presence of renal failure presents a particular diagnostic dilemma, as renal failure itself can lead to a similar constellation of abnormalities. The magnitude of aldosterone elevation may be the key (ie, aldosterone is only about 2-3 times normal with renal failure).

A recent report assessed changes of the urinary aldosterone-to-creatinine ratio in normal cats in response to increased dietary salt or administration of fludrocortisone acetate (18). In that study, normal cats showed the most consistent decrease of the urinary aldosterone-to-creatinine ratio with administration of fludrocortisone acetate as compared with dietary salt supplementation. One cat with an aldosterone-secreting adrenal carcinoma had an elevated ratio and no suppression in response to fludrocortisone acetate. Such mineralocorticoids function tests may prove useful as more cats are diagnosed with this syndrome.

Initial treatment of cats with hyperaldosteronism should be directed toward provision of parenteral or oral potassium supplementation and correction of any fluid deficits and acid-base imbalances. For this purpose, potassium gluconate is generally given at the dosage of 2-6 mEq/day, with the dose adjusted as necessary to maintain normokalemia. If necessary, the diuretic spironolactone, which acts as an aldosterone receptor antagonist, can also be administered at the dosage of 2-4 mg/kg/day.

Surgical adrenalectomy is the treatment of choice in most cats with hyperaldosteronism that do not have evidence of metastatic disease. For those cats that have bilateral adrenal hyperplasia, metastatic disease, or whose owners have declined surgery, medical management with oral spironolactone and potassium can be continued indefinitely.


Catecholamine Secreting Adrenal Tumors
Pheochromocytoma is a catecholamine-producing tumour derived from the chromaffin cells of the adrenal medulla that is extremely rare in cats (1, 2). Clinical signs and physical examination findings develop as a result of the space-occupying nature of the tumour and its metastases, or as a result of excessive secretion of catecholamines and their impact on blood pressure and cardiac function. A diagnosis of pheochromocytoma prior to surgery is usually one of exclusion. Unlike a cortisol-secreting adrenal tumour, the contralateral adrenal gland should be normal in size and shape with a catecholamine-producing adrenal tumour. Catecholamine secretion by the tumour, and thus systemic hypertension, tends to be episodic; failure to document systemic hypertension does not rule out pheochromocytoma. Measurement of urinary catecholamine concentrations or their metabolites can strengthen the tentative diagnosis of pheochromocytoma but is not commonly performed in cats. Because many of the clinical signs and blood pressure alterations are similar for pheochromocytoma and adrenal-dependent hyperadrenocorticism, it is important to rule out adrenal-dependent hyperadrenocorticism before focusing on pheochromocytoma.

References
1. Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.

2. Peterson ME, Randolph JF, Mooney CT. Endocrine diseases. In: Sherding RG eds. The Cat: Siagnosis and Clinical Management (2nd ed). New York: Churchill Livingstone, 1984; 1404-1506.
3. Duesberg C. Peterson ME. Adrenal disorders in cats. Vet Clin North Am Small Anim Pract 1997;27:321-347.

4. Peterson ME. Feline hyperadrenocorticism. In: Mooney CT, Peterson ME (eds). BSAVA Manual of Endocrinology (Third Ed), Quedgeley, Gloucester, British Small Animal Veterinary Association, pp 205-212, 2004.

5. Duesberg CA, Nelson RW, Feldman EC, et al. Adrenalectomy for treatment of hyperadrenocorticism in cats: 10 cases (1988-1992). J Am Vet Med Assoc 1995;207:1066-1070.

6. Boag AK, Neiger R, Church DB. Trilostane treatment of bilateral adrenal enlargement and excessive sex steroid hormone production in a cat. J Small Anim Pract 2004;45: 263-266.

7. Boord M, Griffin C. Progesterone-secreting adrenal mass in a cat with clinical signs of hyperadrenocorticism. J Am Vet Med Assoc 1999; 214: 666-669.

8. Rossmeisl JH, Scott-Moncrieff JC, Siems J, et al. Hyperadrenocorticism and hyper-progesteronemia in a cat with an adrenocortical adenocarcinoma. J Am Anim Hosp Assoc 2000; 36: 512-517.

9. Declue AE, Breshears LA, Pardo ID, et al: Hyperaldosteronism and hyperprogesteronism in a cat with an adrenal cortical carcinoma. J Am Vet Med Assoc 2005:19: 355-358.

10. Quante S, Sieber-Ruckstuhl N, Wilhelm S, et al. Hyperprogesteronism due to bilateral adrenal carcinomas in a cat with diabetes mellitus. Schweizer Archiv fur Tierheilkunde 2009; 151: 437-442.

11. Millard RP, Pickens EH, Wells KL. Excessive production of sex hormones in a cat with an adrenocortical tumour. J Am Vet Med Assoc. 2009;234:505-508.

12. Briscoe K, Barrs VR, Foster DF, et al. Hyperaldosteronism and hyperprogesteronism in a cat. J Fel Med Surg 2009; 11: 758-762.

13. Rose SA, Kyles AE, Labelle P. Adrenalectomy and caval thrombectomy in a cat with primary hyperaldosteronism. J Am Anim Hosp Assoc. 2007; 43: 209-214.

14. Ash RA, Harvey Am, Tasker S. Primary hyperaldosteronism in the cat: a series of 13 cases. J Feline Med Surg 2005; 7: 173-82.

15. Gunn-Moore D. Feline endocrinopathies. Vet Clin North Am Small Anim Pract 2005; 35: 171-210.

16. Rijnberk A, Voorhout G, Kooistra HS, et al: Hyperaldosteronism in a cat with metastasised adrenocortical tumour. Vet Q 2001; 23: 38-43.

17. Javadi S, Djajadiningrat-Laanen SC, Kooistra HS et al. Primary hyperaldosteronism, a mediator of progressive renal disease in cats. Domestic Animal Endocrinol 2005; 28: 85-104.

18. Djajadiningrat-Laanen SC, Galac S, Cammelbeeck SE, et al. Urinary aldosterone to creatinine ratio in cats before and after suppression with salt or fludrocortisone acetate. J Vet Intern Med 2008;22:1283-2388.