Working Up Cats with an Adrenal Mass

I have a 14 year old DSH cat that has been diagnosed with a 3 cm unilateral adrenal mass by ultrasound. Her triglyceride level has been rising consistently for the past 6 months, and she also has had a history of hypertension and mild hypokalemia that responds only to high dose of Tumil K. 

The cat also has early (Stage 2) chronic renal disease with low urine SG, but otherwise she is pretty healthy. She has no weight loss, diabetes mellitus, or thinning of skin. The only change that the owner reports is increased vocalization and a voracious appetite.

Her owner is considering adrenal surgery, but in case this is not an option, I would like to know about your experience in using trilostane as a medical treatment option, assuming Cushing's syndrome is confirmed.

If the owner does elect for surgery, is it still important to find out what the adrenal mass is secreting?

My Response:
From the cat's history and laboratory work (hypertension and hypokalemia), it sounds like hyperaldosteronism (Conn's syndrome) is most likely in this case (1,2). I'd certainly try to determine what hormone(s) are being secreted by the adrenal mass in order to help in peri-operative care of this cat.

Knowing the tumor's hormone secretion pattern prior to surgery is important in the management of the adrenal tumor. For example, if this cat does have Cushing's syndrome secondary to a cortisol-secreting adrenal mass, the function of the contralateral adrenal gland would be suppressed and postoperative adrenal insufficiency would be expected (3-5). If the cat has a pheochromocytoma, severe hypertension or cardiac arrhythmia could develop during surgery so we ideally would prepare them for surgery with phenoxybenzamine (6,7).

I'd start by measuring a basal aldosterone secretion to help diagnose or rule out Conn's syndrome (1,2). If that is borderline or normal, I'd do a dexamethasone screening test next to rule out hyperadrenocorticism. For cats, we use a dexamethasone dose of 0.1 mg/kg, IV, with cortisol samples collected before, 4, and 8 hours after the dexamethasone injection (8,9). Pheochromocytoma is more difficult to diagnose, but measurement of plasma or urine levels of catecholamines might be helpful (10-12). However, little work has been done in cats with pheochromocytoma, largely due to the fact that this is a very rare adrenal tumor in cats.

Examination of adrenal gland size with ultrasound can also help differentiate cats with Cushing's syndrome due to cortisol-secreting tumor from those with Conn's syndrome or pheochromocytoma. In cats with a unilateral cortisol-secreting tumor, we would expect the contralateral adrenal gland to atrophy as a result of suppression of pituitary ACTH secretion; therefore, the adrenal tumor would be larger than normal, whereas the contralateral adrenal should be small (9,13,14). In cats with Conn's or pheochromocytoma, the size of the contralateral adrenal gland generally remains with normal limits (2,13,14).

If the cat does indeed have Cushing's syndrome, trilostane (Vetoryl) may certainly help to control the excessive cortisol secretion by the adrenal mass. The dose need is quite variable, and can range from 10 mg up to 60 mg per day (9). Obviously, trilostane would not have any effect on hormone secretion if the cat has an aldosterone or catecholamine-secreting tumor.

References:

1. Djajadiningrat-Laanen S, Galac S, Kooistra H. Primary hyperaldosteronism: expanding the diagnostic net. J Feline Med Surg 2011;13:641-650. 
2. Harvey AM, Refsal KR. Feline hyperaldosteronism In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Fourth ed. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012;204-214.
3. Peterson ME, Birchard SJ, Mehlhaff CJ. Anesthetic and surgical management of endocrine disorders. Vet Clin North Am Small Anim Prac 1984;14:911-925. 
4. 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.
5. Peterson ME. Feline hypoadrenocorticism In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Fourth ed. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012;190-198.
6. Maher ER, Jr., McNiel EA. Pheochromocytoma in dogs and cats. Vet Clin North Am Small Anim Pract 1997;27:359-380. 
7. Herrera MA, Mehl ML, Kass PH, et al. Predictive factors and the effect of phenoxybenzamine on outcome in dogs undergoing adrenalectomy for pheochromocytoma. J Vet Intern Med 2008;22:1333-1339. 
8. Duesberg C, Peterson ME. Adrenal disorders in cats. Vet Clin North Am Small Anim Pract 1997;27:321-347. 
9. 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.
10. Gostelow R, Bridger N, Syme HM. Plasma-free metanephrine and free normetanephrine measurement for the diagnosis of pheochromocytoma in dogs. J Vet Intern Med 2013;27:83-90. 
11. Quante S, Boretti FS, Kook PH, et al. Urinary catecholamine and metanephrine to creatinine ratios in dogs with hyperadrenocorticism or pheochromocytoma, and in healthy dogs. J Vet Intern Med 2010;24:1093-1097. 
12. Kook PH, Grest P, Quante S, et al. Urinary catecholamine and metadrenaline to creatinine ratios in dogs with a phaeochromocytoma. Vet Rec 2010;166:169-174. 
13. Barthez PY, Nyland TG, Feldman EC. Ultrasonography of the adrenal glands in the dog, cat, and ferret. Vet Clin North Am Small Anim Pract 1998;28:869-885. 
14. Tidwell AS, Penninck DG, Besso JG. Imaging of adrenal gland disorders. Vet Clin North Am Small Anim Pract 1997;27:237-254.