What Is Cushing’s Disease in Dogs?
Cushing’s disease — medically known as hyperadrenocorticism — is one of the most common endocrine (hormonal) disorders in dogs, occurring when the body produces an excess of cortisol. Cortisol is produced by the adrenal glands and plays vital roles in metabolism, immune response, and stress management. When cortisol is chronically elevated, it disrupts nearly every system in the body. Cushing’s disease is most commonly diagnosed in middle-aged to senior dogs over the age of six, and its symptoms — many overlapping with normal ageing — are often initially dismissed, meaning many dogs go undiagnosed for months or years. There are three forms: pituitary-dependent (PDH, 85–90% of cases), adrenal-dependent (ADH, 10–15%), and iatrogenic (caused by external steroid medication).
Causes of Cushing’s Disease in Dogs
Pituitary-Dependent Hyperadrenocorticism (PDH) — the most common form — is caused by a usually benign tumour of the pituitary gland at the base of the brain. The tumour secretes excess ACTH (adrenocorticotropic hormone), which signals the adrenal glands to continuously overproduce cortisol, causing both adrenal glands to enlarge. Adrenal-Dependent Hyperadrenocorticism (ADH) is caused by a tumour on one adrenal gland — which may be benign or malignant — autonomously producing excess cortisol. Iatrogenic Cushing’s Disease occurs when a dog receives excessive glucocorticoid medications such as prednisone for an extended period; this form resolves when steroids are gradually withdrawn under veterinary supervision. Breeds predisposed to PDH include Poodles (Miniature and Toy), Dachshunds, Boston Terriers, Boxers, and Beagles.
Symptoms of Cushing’s Disease in Dogs
The hallmark symptoms develop gradually and are easy to mistake for normal ageing. Most noticeable are polydipsia and polyuria (excessive drinking and urination), often the first signs. Polyphagia (excessive hunger) makes dogs seem insatiably hungry. A pot-bellied abdomen develops due to muscle weakness, fat redistribution, and liver enlargement. Bilateral symmetrical hair loss and coat thinning spare the face and limbs. Skin changes include thinning, fragile skin that bruises easily, comedones (blackheads), and hyperpigmentation. Muscle weakness and lethargy lead to exercise intolerance and difficulty jumping. Panting at rest or in cool temperatures is common. Recurrent urinary tract infections and skin infections result from immunosuppression. Calcinosis cutis — calcium deposits forming firm white plaques under the skin — may also develop in advanced cases.
Diagnosing Cushing’s Disease in Dogs
Diagnosing Cushing’s disease requires a combination of tests — there is no single definitive test. Blood chemistry panels typically show elevated alkaline phosphatase (ALP), high cholesterol and triglycerides, and elevated blood glucose. The Urine Cortisol to Creatinine Ratio (UCCR) is a useful screening test with high sensitivity but many false positives. The Low-Dose Dexamethasone Suppression Test (LDDST) is the most sensitive confirmatory test — dexamethasone is injected and blood cortisol measured at 4 and 8 hours; in Cushing’s disease, cortisol suppression is inadequate. The ACTH Stimulation Test is most useful for monitoring treatment response. Abdominal ultrasound helps identify adrenal gland enlargement and assess liver changes.
Treatment Options and Long-Term Management
Medical treatment is most common for PDH. Trilostane (Vetoryl) inhibits an enzyme required for cortisol synthesis and is the most widely used drug in many countries. Mitotane (Lysodren) is an alternative. Both require regular monitoring and careful dose adjustment — the goal is to control cortisol without inducing Addison’s disease (cortisol deficiency), which can be life-threatening. Regular ACTH stimulation tests every 3–6 months are essential throughout treatment. Surgical adrenalectomy (removal of the affected adrenal gland) is the treatment of choice for ADH caused by a benign adrenal tumour and can be curative, though it carries significant surgical risk. Iatrogenic Cushing’s resolves when the offending steroid medication is slowly tapered under veterinary supervision. With appropriate treatment, most dogs achieve good quality of life for years after diagnosis.
What are the first signs of Cushing’s disease in dogs?
The earliest and most common signs are excessive drinking and urination (polydipsia/polyuria), increased appetite, and increased panting. Many owners initially attribute these to ageing. As the disease progresses, a pot-bellied appearance, symmetrical hair loss, skin thinning, and lethargy become apparent, typically over 12–18 months.
Can Cushing’s disease in dogs be cured?
Cushing’s disease caused by a benign adrenal tumour (ADH) can be cured through surgical removal. The more common pituitary-dependent form (PDH) is generally managed long-term with medications like trilostane, which control cortisol levels but do not eliminate the pituitary tumour. Iatrogenic Cushing’s resolves when steroid medications are gradually discontinued.
How long can a dog live with Cushing’s disease?
With appropriate medical management, many dogs with Cushing’s disease live comfortable, good-quality lives for two or more years after diagnosis, and some live much longer. Untreated Cushing’s disease significantly increases the risk of complications including urinary tract infections, blood clots, hypertension, and diabetes mellitus.
What breeds are most prone to Cushing’s disease?
Miniature and Toy Poodles, Dachshunds, Boston Terriers, Boxers, Beagles, and Yorkshire Terriers have a documented higher prevalence of pituitary-dependent Cushing’s disease. Any breed including mixed breeds can develop the condition. The average age of diagnosis is around 10 years.
Is Cushing’s disease painful for dogs?
Cushing’s disease itself is not typically painful, but secondary effects significantly impact quality of life. Muscle weakness makes movement difficult and uncomfortable, skin lesions and infections can cause discomfort, and many dogs appear uncomfortable due to excessive panting and restlessness. Appropriate medical management substantially improves quality of life.