Cushing's Syndrome in Dogs: Symptoms, Diagnosis, and Treatment
Cushing's Syndrome in Dogs: Symptoms, Diagnosis, and Treatment
What is Cushing's syndrome in dogs?
Cushing's syndrome (hyperadrenocorticism, HAK) is a condition in which excess cortisol circulates in the blood on a long-term basis. Cortisol is a stress hormone produced by the adrenal cortex—essential in moderation, but harmful to nearly every system in the body when overproduced over time. It is one of the most common hormonal disorders in dogs, typically affecting older animals (> 6 years) and developing gradually over months to years.
There are two spontaneous forms: pituitary-dependent HAK (80–85% of cases, in which a pituitary tumor stimulates excessive cortisol production) and adrenal-dependent HAK (15–20%, in which an adrenal tumor autonomously produces cortisol).
Background + Scientific Context
Feldman and Nelson (2004, *Canine and Feline Endocrinology and Reproduction*) describe the pathogenesis and clinical presentation: Chronic excess cortisol has a catabolic effect—it breaks down muscle and connective tissue, suppresses the immune system, alters fat and glucose metabolism, and disrupts skin and coat structure. Classic symptoms: polyuria/polydipsia (PU/PD, excessive drinking and urination), polyphagia (voracious appetite), symmetrical alopecia without itching (bilateral hair loss on the trunk), potbelly (hepatomegaly, abdominal fat redistribution), thin, cracked skin with comedones, muscle weakness (hind legs affected first). Breed predisposition: Poodles, Dachshunds, Boxers, Boston Terriers, Beagles — small and medium breeds are significantly overrepresented.
Behrend et al. (2013, ACVIM Consensus Statement, https://pubmed.ncbi.nlm.nih.gov/24112079/) describe the diagnostic standards: No single test can definitively rule out or confirm Cushing’s disease—multiple tests are combined. Urine cortisol-to-creatinine ratio (UCCR) as a screening tool: high sensitivity, low specificity. ACTH stimulation test: measures adrenal reserve—an elevated cortisol response confirms HAK. LDDS (Low-Dose Dexamethasone Suppression Test): Gold standard for diagnosis and differentiation between pituitary-dependent and adrenal-dependent forms. Adrenal ultrasound: bilateral hyperplasia (in PDH) vs. unilateral tumor (in AT). CT or MRI for detection of pituitary tumors in cases of large tumors.
Ettinger et al. (2017, *Textbook of Veterinary Internal Medicine*) describe treatment options: Trilostane (Vetoryl) is the first-line therapy for PDH and AT—it reversibly inhibits adrenal cortisol synthesis and is administered orally once daily. Monitoring is performed using an ACTH stimulation test 10 days after the start of therapy, then every 3–6 months. Mitotane (Lysodren) as an alternative therapy—selectively destroys the adrenal cortex, higher risk of side effects, less commonly used. Adrenalectomy for solitary adrenal tumors (AT) is curative. Iatrogenic Cushing’s syndrome (due to long-term corticosteroid administration): taper off the corticosteroid.
Vitomalia-Position
Cushing's disease develops so slowly that many owners mistake its symptoms for signs of aging—PU/PD, a sagging belly, and hair loss. Diagnosis is challenging and expensive. Treatment is long-term and requires regular monitoring. Early detection can give a dog many more years of life with a good quality of life.
When does Cushing's syndrome become a concern?
- Older dog (> 6 years) with increased water intake and frequent urination
- Symmetrical hair loss without itching on the body of an older dog
- A potbelly despite a normal body weight
- Dog is eating excessively without gaining weight
- The skin becomes thin and cracked, with comedones (blackheads)
- Recurrent urinary tract infections (cortisol-induced immunosuppression)
Practical application
An Overview of Cushing's Symptoms:
| Symptom | Mechanism | Frequency |
|---|---|---|
| PU/PD (drink plenty of fluids/urinate frequently) | Cortisol inhibits the action of ADH | > 80% of cases |
| Polyphagia (gluttony) | Cortisol stimulates the appetite center | > 80% |
| potbelly | Hepatomegaly + fat redistribution | > 70% |
| Symmetrical alopecia | Catabolism of hair follicles | > 60% |
| Muscle weakness | Cortisol's Catabolic Effects on Muscle | > 50% |
| Thin skin, blackheads | Effect of cortisol on the dermis | > 40% |
Diagnostic algorithm (simplified): 1. Clinical suspicion + baseline blood tests (elevated ALT, ALP, blood glucose) 2. UCCR as a screening test — normal = Cushing's syndrome unlikely 3. ACTH stimulation test or LDDS — Confirmation 4. Abdominal ultrasound — Distinguishing between PDH and AT 5. Start of treatment with trilostane; ACTH monitoring after 10 days
Common Mistakes & Myths
- "It's normal for older dogs to drink more." Polyuria and polydipsia are never normal—they are warning signs of several medical conditions (Cushing's disease, diabetes mellitus, kidney failure, pyometra). Always consult a veterinarian.
- "Cushing's syndrome is only recognizable by hair loss." Polyuria, polydipsia, and polyphagia are earlier and more common signs than hair loss. Many cases are first detected through abnormalities found in routine blood tests.
- "If the dog is stable on trilostane, it does not require monitoring." Trilostane can lead to an Addisonian crisis (cortisol deficiency)—regular ACTH tests are mandatory, even for stable dogs. Without monitoring, there is a life-threatening risk.
Current State of Research (2026)
Trilostane is the standard of care for canine hyperadrenocorticism. Recent studies have optimized dosing and monitoring intervals. Brain MRI is important for assessing prognosis in symptomatic pituitary tumors (neurological signs). Adrenalectomy for AT yields excellent long-term results. Genome-wide association studies have identified genetic predispositions in certain breeds.
Frequently Asked Questions
What are the symptoms of Cushing's syndrome in dogs?
Classic signs: excessive drinking and urination (PU/PD), voracious appetite, potbelly, symmetrical hair loss on the trunk without itching, thin skin, and muscle weakness. The symptoms develop gradually over months or years and are often mistaken for signs of aging.
How is Cushing's syndrome diagnosed in dogs?
By combining the following: UCCR for screening, an ACTH stimulation test or LDDS for confirmation, and ultrasound to distinguish between pituitary Cushing’s disease (PDH) and an adrenal tumor (AT). No single test is conclusive on its own—the diagnosis is a multi-step process.
How is Cushing's disease treated in dogs?
Pituitary-dependent Cushing's syndrome (PDH): Trilostane (Vetoryl) administered orally once daily — reversibly inhibits cortisol synthesis. Regular ACTH monitoring is mandatory. Adrenal tumor (AT): Adrenalectomy is curative. Iatrogenic Cushing's syndrome: Gradually taper off the corticosteroid.
Related terms
Sources & Further Reading
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Feldman, E. C., & Nelson, R. W. (2004). Canine and Feline Endocrinology and Reproduction (3rd ed.). Saunders. ISBN 9780721693156.
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Behrend, E. N., Kooistra, H. S., Nelson, R., Reusch, C. E., & Scott-Moncrieff, J. C. (2013). Diagnosis of spontaneous canine hyperadrenocorticism: 2012 ACVIM consensus statement. Journal of Veterinary Internal Medicine, 27(6), 1292–1304. https://pubmed.ncbi.nlm.nih.gov/24112079/
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Ettinger, S. J., Feldman, E. C., & Côté, E. (Eds.) (2017). Textbook of Veterinary Internal Medicine (8th ed.). Saunders. ISBN 9780323312110.