Cushing’s disease, formally known as hyperadrenocorticism, is a common endocrine disorder in middle-aged and older dogs. It results from chronic overproduction of cortisol by the adrenal glands. Cortisol is essential for normal body functions in small amounts, but chronically elevated levels affect nearly every organ system and significantly reduce quality of life. Cushing’s disease is manageable with medication in most cases, but it requires careful monitoring and close collaboration with your veterinarian.
Overview
There are three forms of Cushing’s disease in dogs:
- Pituitary-dependent hyperadrenocorticism (PDH) — Accounts for approximately 80-85% of cases. A benign tumor (microadenoma or macroadenoma) in the pituitary gland at the base of the brain produces excessive ACTH, which stimulates both adrenal glands to overproduce cortisol.
- Adrenal-dependent hyperadrenocorticism — Accounts for approximately 15-20% of cases. A tumor on one adrenal gland (which may be benign or malignant) independently produces excess cortisol.
- Iatrogenic Cushing’s syndrome — Caused by long-term administration of exogenous corticosteroids (such as prednisone). Resolving this form requires gradual tapering of the steroid under veterinary supervision.
Cushing’s disease most commonly affects dogs over 6 years of age. Predisposed breeds include Poodles, Dachshunds, Boston Terriers, Boxers, Beagles, and Yorkshire Terriers, though any breed can be affected.
Symptoms
The signs of Cushing’s disease develop gradually and are often initially attributed to aging. Classic symptoms include:
- Increased thirst (polydipsia) and increased urination (polyuria) — often the most noticeable early sign
- Increased appetite (polyphagia) — dogs may become ravenous or begin counter-surfing
- Pot-bellied appearance due to abdominal muscle weakness and fat redistribution
- Panting, even at rest
- Bilateral symmetrical hair loss (alopecia) — often on the trunk, sparing the head and legs
- Thin, fragile skin that bruises easily
- Recurrent skin infections or urinary tract infections
- Calcinosis cutis (calcium deposits in the skin)
- Muscle weakness and exercise intolerance
- Failure of hair to regrow after clipping
If you notice several of these signs in your dog, particularly the combination of excessive drinking, urination, and a pot-bellied appearance, consult your veterinarian.
Diagnosis
Diagnosing Cushing’s disease involves multiple steps because no single test is definitive:
- Routine bloodwork and urinalysis — Dogs with Cushing’s often show elevated liver enzymes (especially alkaline phosphatase), elevated cholesterol, dilute urine (low specific gravity), and sometimes elevated blood glucose. These findings raise suspicion but are not diagnostic.
- Urine cortisol:creatinine ratio (UCCR) — A screening test collected at home. A normal result makes Cushing’s very unlikely, but an elevated result requires further testing (the test is sensitive but not specific).
- Low-dose dexamethasone suppression test (LDDS) — Considered the screening test of choice by many internists. A blood cortisol level is measured, dexamethasone is administered, and cortisol is remeasured at 4 and 8 hours. Normal dogs suppress cortisol production; dogs with Cushing’s typically do not.
- ACTH stimulation test — Measures the adrenal glands’ response to synthetic ACTH. Less sensitive than the LDDS test but more specific. Also used to monitor trilostane therapy.
- High-dose dexamethasone suppression test — Helps differentiate pituitary-dependent from adrenal-dependent disease.
- Abdominal ultrasound — Evaluates adrenal gland size and symmetry. Bilaterally enlarged adrenal glands suggest PDH, while a single enlarged gland with an atrophied opposite gland suggests an adrenal tumor.
- Advanced imaging (CT or MRI) — May be recommended to evaluate pituitary tumor size, especially if neurological signs are present.
Treatment & Medications
Treatment depends on the type of Cushing’s disease. Your veterinarian will develop a plan specific to your dog.
| Medication | Type | How It Works | Key Notes |
|---|---|---|---|
| Trilostane (Vetoryl) | Adrenal enzyme inhibitor | Reversibly blocks cortisol synthesis in the adrenal glands | Current first-line treatment for both PDH and adrenal-dependent Cushing’s. Given once or twice daily with food. Requires ACTH stimulation testing for dose adjustments. |
| Mitotane (Lysodren) | Adrenolytic agent | Selectively destroys cortisol-producing cells in the adrenal cortex | Effective but carries a higher risk of serious side effects including adrenal crisis. Used less frequently since trilostane became available. Requires careful induction and maintenance phases. |
| Selegiline (Anipryl) | MAO-B inhibitor | Reduces ACTH secretion from the pituitary | FDA-approved for canine PDH but generally considered less effective than trilostane or mitotane. May be considered for mild cases. |
Surgical Options
- Adrenalectomy — Surgical removal of an adrenal tumor is potentially curative for adrenal-dependent Cushing’s disease, but the surgery is complex and carries significant risk. Should be performed by a board-certified veterinary surgeon.
- Hypophysectomy — Surgical removal of the pituitary tumor. Available at a very limited number of veterinary referral centers.
Iatrogenic Cushing’s
If Cushing’s syndrome is caused by long-term steroid use, the treatment is gradual tapering of the corticosteroid under veterinary guidance. Abrupt discontinuation can cause a life-threatening Addisonian crisis.
Monitoring
Dogs on trilostane require regular monitoring, especially during the first few months:
- ACTH stimulation test — Typically performed 10 to 14 days after starting trilostane or after any dose change, then every 3 to 6 months once stable. The blood sample must be drawn 4 to 6 hours after the morning trilostane dose.
- Electrolyte monitoring — Sodium and potassium levels should be checked, as trilostane can occasionally cause Addisonian-like effects.
- Clinical symptom assessment — Water intake, urination frequency, appetite, and energy level are important markers of treatment response.
- Emergency awareness — Signs of cortisol levels dropping too low (Addisonian crisis) include vomiting, diarrhea, lethargy, weakness, and collapse. This is a medical emergency requiring immediate veterinary attention.
Prognosis
With appropriate treatment and monitoring, many dogs with Cushing’s disease live comfortably for 2 to 3 years or longer after diagnosis. Prognosis varies based on:
- PDH — Generally favorable with medical management. Dogs typically show improvement in drinking, urination, and appetite within weeks. Skin and coat improvements take longer (months).
- Adrenal tumors — Prognosis depends on whether the tumor is benign or malignant. Benign adrenal tumors may be curable with surgery. Malignant adrenal tumors (adrenal carcinomas) carry a more guarded prognosis.
- Large pituitary tumors (macroadenomas) — May cause neurological signs as they grow, which worsens the prognosis.
Untreated Cushing’s disease predisposes dogs to serious secondary conditions including diabetes mellitus, pancreatitis, pulmonary thromboembolism, and hypertension.
Frequently Asked Questions
Can Cushing’s disease be cured? Adrenal-dependent Cushing’s may be cured with surgical removal of the affected adrenal gland, provided the tumor is benign and surgery is successful. Pituitary-dependent Cushing’s is typically managed medically rather than cured.
How quickly does trilostane work? Most owners notice improvement in excessive drinking and urination within the first 1 to 2 weeks. Full clinical improvement, including skin and coat changes, may take several months.
Is trilostane safe? Trilostane is generally well tolerated when used with appropriate monitoring. The most serious risk is excessive cortisol suppression (iatrogenic hypoadrenocorticism), which is why regular ACTH stimulation testing is essential. Always give trilostane with food and contact your veterinarian if your dog becomes lethargic, stops eating, or develops vomiting or diarrhea.
My dog has both Cushing’s disease and diabetes. Are they related? Yes, Cushing’s disease can cause or worsen diabetes mellitus because excess cortisol antagonizes insulin. Treating the Cushing’s disease often improves or resolves the diabetes. Your veterinarian will coordinate management of both conditions.
Should I stop trilostane if my dog is having surgery or is ill? Consult your veterinarian before making any changes to trilostane dosing. In some situations, the medication may be temporarily held, but this decision should always be made by your veterinarian.