Cushing's Disease in Dogs: A Complete Owner's Guide

What Is Cushing's Disease?

Hyperadrenocorticism — Cushing's disease — is a hormonal disorder caused by chronic excess cortisol. In 85-90% of cases, it results from a pituitary tumor that overproduces ACTH (pituitary-dependent hyperadrenocorticism, PDH). In the remaining cases, a cortisol-producing adrenal tumor is the cause (adrenal-dependent hyperadrenocorticism). A third cause is iatrogenic Cushing's — caused by long-term steroid medication administration. Cushing's is one of the most common endocrine disorders in dogs, occurring most often in middle-aged to older dogs of various breeds, with Poodles, Dachshunds, Boxers, and small mixed breeds overrepresented.

Recognizing the Signs

The classic Cushing's dog has a recognizable profile: PU/PD (polydipsia/polyuria — drinking and urinating dramatically more than normal), polyphagia (increased appetite that can seem insatiable), pot-bellied appearance (from fat redistribution and muscle wasting), bilateral symmetric hair loss (coat thinning, particularly on the trunk), thin and fragile skin, lethargy, panting more than normal, and susceptibility to skin infections. Not all dogs show all signs, and some signs (panting, lethargy) are easily attributed to age.

Diagnosis

Diagnosis requires confirmatory testing, as clinical signs alone can overlap with other conditions. The LDDS (low-dose dexamethasone suppression test) and the ACTH stimulation test are the primary screening tests. The ACTH stimulation test is also used to monitor treatment. Differentiating PDH from adrenal tumor requires either an HDDS (high-dose DST) or abdominal ultrasound looking for adrenal gland abnormalities.

Treatment

PDH is treated medically with trilostane (Vetoryl) or mitotane (Lysodren), both of which suppress cortisol production. These medications require careful monitoring — Addisonian crisis (cortisol deficiency) is a serious complication of overtreatment. Adrenal tumors may be surgically removed (a specialized procedure with significant risk but potential for cure). Life expectancy with well-managed Cushing's is good; quality of life improves substantially with successful treatment as the insatiable thirst, inappropriate urination, lethargy, and skin issues resolve.