Hyperadrenocorticism (Cushing's Syndrome) in Cats: Why It Hides Behind Diabetes and How to Find It

Hyperadrenocorticism — Cushing's syndrome — is uncommon in cats, and that rarity is part of what makes it dangerous. Over 90% of cats diagnosed with Cushing's also have diabetes mellitus, and many are simply labeled "difficult-to-regulate diabetics" for months before anyone looks deeper. The average age at diagnosis is 10 to 11 years, and roughly 70% of affected cats are female (Merck Veterinary Manual, 2024). In about 80% of cases, a small pituitary tumor drives both adrenal glands to overproduce cortisol, breaking down skin, suppressing immunity, and making diabetes nearly impossible to control (AAHA, 2023).

Why is Cushing's syndrome so much harder to spot in cats than in dogs?

Hyperadrenocorticism — Cushing's syndrome — is uncommon in cats, and that rarity is part of what makes it dangerous. In dogs, the classic signs of a pot-bellied appearance, symmetrical hair loss, and excessive drinking are well known to most veterinarians. In cats, the disease often hides behind a wall of concurrent diabetes mellitus. Over 90% of cats diagnosed with Cushing's syndrome also have diabetes, and many of those cats are simply labeled "difficult-to-regulate diabetics" for months before anyone looks deeper (AAHA, 2023). The average age at diagnosis is 10 to 11 years, and roughly 70% of affected cats are female, with no breed predilection (Merck Veterinary Manual, 2024).

In about 80% of feline cases, a small, usually benign tumor of the pituitary gland at the base of the brain secretes excess adrenocorticotropic hormone (ACTH), which in turn drives both adrenal glands to overproduce cortisol. This is pituitary-dependent hyperadrenocorticism. The remaining 20% of cases arise from a tumor of the adrenal cortex itself — adrenal-dependent disease — which may be benign or malignant (International Cat Care, 2024). Regardless of origin, the result is the same: chronically elevated glucocorticoids that break down skin, suppress the immune system, and antagonize insulin, making diabetes nearly impossible to control.

What does a cat with undiagnosed Cushing's actually look like at home?

The skin is often the first organ to betray the disease. Cats develop extreme cutaneous fragility — skin that tears with routine handling, resists healing, and bruises under minimal pressure. Symmetrical hair loss over the flanks and abdomen is common, and the coat becomes dull, thin, and unkempt. Owners may notice their cat developing a pendulous, pot-bellied abdomen despite generalized muscle wasting over the spine and hindquarters (AAHA, 2023). These cats look older than their years, and they often carry recurrent skin, urinary tract, or respiratory infections that antibiotics cannot seem to clear.

Because the overwhelming majority of these cats are also diabetic, the household story usually includes a water bowl that empties faster than expected, a litter box that needs changing twice as often, and a cat that is ravenously hungry yet losing weight. Insulin doses climb without meaningful improvement in blood glucose, and the cat cycles through episodes of diabetic ketoacidosis. A cat on escalating insulin doses with poor glycemic control and fragile skin should trigger an immediate workup for hyperadrenocorticism (Merck Veterinary Manual, 2024).

Which diagnostic tests actually confirm Cushing's in a cat?

No single test is perfect, and the diagnosis rests on a combination of clinical suspicion, screening tests, and imaging. Baseline blood work may reveal a stress leukogram, elevated liver enzymes (particularly alkaline phosphatase), and persistent hyperglycemia. Urinalysis often confirms glucosuria and may show a concurrent urinary tract infection. The ACTH stimulation test is commonly used as a screening tool: a cat with hyperadrenocorticism typically shows an exaggerated cortisol response after synthetic ACTH administration. However, false negatives occur, and some cats require a low-dose dexamethasone suppression test (LDDST) for confirmation (AAHA, 2023).

Abdominal ultrasound is essential. In pituitary-dependent disease, both adrenal glands are symmetrically enlarged. In adrenal-dependent disease, one gland is enlarged and the contralateral gland is often atrophied. Advanced imaging — CT or MRI — can identify a pituitary mass and help determine whether surgical intervention is feasible. Because feline Cushing's is so rare, referral to an internal medicine specialist is strongly recommended before committing to a lifelong treatment plan (International Cat Care, 2024).

What treatment options actually work for cats with Cushing's syndrome?

Treatment in cats is more limited than in dogs, and surgery remains the treatment of choice when feasible. For pituitary-dependent disease, bilateral adrenalectomy removes the source of cortisol overproduction, but it leaves the cat permanently adrenally insufficient and dependent on lifelong glucocorticoid and mineralocorticoid supplementation. For unilateral adrenal tumors, adrenalectomy of the affected gland can be curative if the tumor is benign and has not invaded local vessels (Merck Veterinary Manual, 2024).

Medical therapy has historically been disappointing. Mitotane (o,p'-DDD) and ketoconazole, which are mainstays of canine Cushing's treatment, are generally ineffective in cats. Trilostane, a reversible 3-beta-hydroxysteroid dehydrogenase inhibitor, has shown more promise in recent years, though published feline data remain limited. Metyrapone has been used with occasional success. Any cat started on medical therapy requires frequent monitoring of electrolytes, cortisol levels, and diabetic control, and owners should expect a period of dose adjustment that may last weeks to months (AAHA, 2023).

What does the long-term outlook look like for a cat with Cushing's?

The prognosis is guarded. Many cats are diagnosed late, after months of poorly controlled diabetes and progressive skin deterioration. Cats that undergo successful adrenalectomy and survive the perioperative period can have a good quality of life, though they require diligent lifelong hormone replacement. Cats managed medically often achieve partial control, and the primary goal shifts from cure to comfort: stabilizing the diabetes, healing the skin, and preventing infections. Median survival times vary widely depending on whether the cat has pituitary or adrenal disease, whether surgery is performed, and how well concurrent diabetes is managed (International Cat Care, 2024).

Owners should understand that feline Cushing's is a chronic, serious disease that demands partnership with a veterinary specialist. The cat that was drinking three bowls of water a day and losing weight despite a ravenous appetite can improve — but improvement is measured in smaller victories: a skin tear that finally heals, an insulin dose that finally holds steady, a week without a new infection.

Cushing's syndrome in cats is far less common than in dogs, and the feline presentation often differs in important ways. While dogs typically show the classic pot-bellied appearance, thinning skin, and excessive drinking, cats with hyperadrenocorticism frequently present with concurrent diabetes mellitus that is difficult to control. In fact, many feline Cushing's cases are first suspected when a diabetic cat requires unexpectedly high insulin doses or shows persistent hyperglycemia despite appropriate management. The overlap between these two endocrine disorders means that veterinarians must consider adrenal function testing whenever a diabetic cat fails to respond to standard insulin protocols (Merck Veterinary Manual, 2025; Cornell University College of Veterinary Medicine, 2021). The diagnosis itself requires careful interpretation because stress alone can elevate cortisol in cats, producing false-positive results on screening tests. For this reason, the dexamethasone suppression test and ACTH stimulation test must be evaluated alongside clinical signs, and sometimes urine cortisol-to-creatinine ratios are used as an initial screening tool before more invasive testing. Treatment options include medical management with trilostane, which inhibits cortisol synthesis, or surgical adrenalectomy when a unilateral adrenal tumor is identified. However, both approaches carry significant risks in cats, and owners should understand that management is often lifelong and requires regular monitoring of electrolytes, cortisol levels, and concurrent diabetic control (Merck Veterinary Manual, 2025).

The prognosis for cats with Cushing's syndrome depends heavily on the underlying cause and the presence of concurrent conditions. Cats with adrenal tumors that can be completely surgically excised have the best long-term outlook, though the surgery itself carries significant risks including hemorrhage, thromboembolism, and postoperative pancreatitis. For cats managed medically with trilostane, regular monitoring of electrolytes, renal function, and clinical signs is essential, as overdosing can lead to life-threatening hypoadrenocorticism. Owners should watch for signs of trilostane overdose including lethargy, vomiting, diarrhea, and collapse, and should have a plan in place for emergency veterinary care if these occur. The management of concurrent diabetes mellitus adds another layer of complexity, as insulin requirements typically decrease once cortisol levels are controlled, and failure to adjust insulin doses accordingly can result in hypoglycemia. Despite these challenges, many cats with well-managed hyperadrenocorticism can enjoy good quality of life for months to years, particularly when the disease is diagnosed early and treatment is tailored to the individual patient (Merck Veterinary Manual, 2025; Cornell University College of Veterinary Medicine, 2021).

References

• American Animal Hospital Association. (2023). Feline hyperadrenocorticism/hypercortisolism. 2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines. https://www.aaha.org/resources/2023-aaha-selected-endocrinopathies-of-dogs-and-cats-guidelines/feline-hyperadrenocorticismhypercortisolism/
• International Cat Care. (2024, June 17). Hyperadrenocorticism (Cushing's disease). https://icatcare.org/articles/hyperadrenocorticism-cushings-disease
• Merck Veterinary Manual. (2024). Cushing syndrome (hyperadrenocorticism) in animals. https://www.merckvetmanual.com/endocrine-system/the-adrenal-glands/cushing-syndrome-hyperadrenocorticism-in-animals