Canine Cushing's Disease: What It Is and How It's Managed

Understanding Hyperadrenocorticism

Cushing’s disease — formally hyperadrenocorticism — results from chronic overproduction of cortisol, the body’s primary stress hormone. In dogs, roughly 85% of cases are pituitary-dependent (a benign pituitary tumor stimulates excess ACTH, which drives the adrenal glands to over-produce cortisol). The remaining 15% are adrenal-dependent (a tumor on the adrenal gland itself produces cortisol autonomously). A third form, iatrogenic Cushing’s, results from prolonged administration of corticosteroid drugs and resolves when the drug is tapered.

Classic Signs

Cushing’s is a slow-developing disease, which means signs often creep up over months or years before an owner notices. Classic presentation: pot-bellied appearance (muscle wasting + fat redistribution), PU/PD (increased thirst and urination), polyphagia (increased appetite, often dramatically), hair loss (bilaterally symmetric, often sparing the head and limbs), thin, fragile skin, and lethargy. Dogs may also develop a pendulous abdomen and exercise intolerance. Recurrent skin infections and urinary tract infections are common secondary problems.

Diagnosis

Screening and confirmatory testing involve hormone measurements: the low-dose dexamethasone suppression test (LDDST) is commonly used. Urinary cortisol-to-creatinine ratio provides a screening option. An ACTH stimulation test is useful for monitoring treatment. Ultrasound of the abdomen evaluates adrenal gland size (bilateral enlargement suggests pituitary-dependent; unilateral suggests adrenal tumor). Diagnosing Cushing’s in a dog with other illnesses can be complicated, as some tests produce false positives in stressed or ill animals.

Treatment

Pituitary-dependent Cushing’s is most commonly treated with trilostane or mitotane, which reduce cortisol production. Both require careful monitoring — over-suppression can cause an Addisonian crisis (dangerously low cortisol). Regular ACTH stimulation tests guide dosing. Adrenal tumors may require surgical removal. Iatrogenic Cushing’s is managed by slowly tapering the corticosteroid under veterinary supervision. With appropriate treatment, most Cushing’s dogs maintain a good quality of life.