Cushing's disease develops gradually in middle-aged to older dogs and is frequently mistaken for normal aging because its symptoms — increased thirst and urination, a pot-bellied appearance, thinning skin, and hair loss — emerge slowly over months. A simple blood and urine screening is usually the first diagnostic step, though confirming the specific type of Cushing's (pituitary-dependent versus adrenal-dependent) requires more advanced testing, since treatment differs significantly between the two. Most dogs respond well to daily oral medication like trilostane, though surgery is sometimes needed for adrenal tumors.
Cushing's disease, medically known as hyperadrenocorticism, is one of the most commonly diagnosed endocrine disorders in middle-aged to older dogs, and occurs less frequently in cats. It develops when the body produces chronically excessive amounts of the stress hormone cortisol, and its symptoms are wide-ranging, slowly progressive, and easily confused with normal aging. This guide explains the causes, the full spectrum of symptoms to recognize, how it is diagnosed, and what treatment and management look like.
What Is Cushing's Disease?
The adrenal glands, two small glands that sit just above the kidneys, produce cortisol, a hormone critical for stress response, immune function, and metabolism. Cushing's disease occurs when this cortisol production becomes unregulated and chronically elevated.
There are two main forms:
- Pituitary-dependent hyperadrenocorticism (PDH): Accounts for approximately 85% of cases. A benign tumor (adenoma) on the pituitary gland produces excess ACTH (adrenocorticotropic hormone), which continuously stimulates both adrenal glands to overproduce cortisol. Both adrenal glands become enlarged.
- Adrenal-dependent hyperadrenocorticism (ADH): Accounts for approximately 15% of cases. A tumor on one adrenal gland, which can be benign or malignant, produces cortisol autonomously, independent of pituitary control. The other adrenal gland typically shrinks (atrophies) due to suppressed ACTH.
- Iatrogenic Cushing's syndrome: Caused by prolonged external administration of corticosteroid medications (prednisone, prednisolone, dexamethasone). Functionally identical to natural Cushing's, resolved by carefully tapering and discontinuing the medication under veterinary supervision.
Which Pets Get Cushing's Disease?
Dogs (Common)
By far the most common species affected. Middle-aged to older dogs, typically 6+ years. Certain breeds are disproportionately affected: Poodles, Dachshunds, Boxers, Boston Terriers, Beagles, and Yorkshire Terriers.
Cats (Uncommon)
Cats develop Cushing's rarely, representing perhaps 1–2% of feline endocrine disease. When it occurs, it is almost always pituitary-dependent and frequently occurs alongside diabetes mellitus that is difficult to regulate.
Ferrets
Adrenal disease is extremely common in ferrets (different from classical Cushing's but related). Most ferrets over 3–4 years old develop adrenal disease; symptoms include hair loss and vulvar enlargement in females.
Reptiles (Rare)
Cortisol-related disorders are rarely diagnosed in reptiles due to diagnostic limitations, but chronic stress in captivity produces many similar effects on reptile physiology.
Symptoms of Cushing's Disease in Dogs
The insidious nature of Cushing's disease is that symptoms develop gradually over months to years, leading many owners to attribute them to normal aging. The classic symptom cluster is highly recognizable once familiar:
| Symptom | How Common | Why It Happens |
|---|---|---|
| Markedly increased thirst and urination (PU/PD) | 90%+ of cases | Excess cortisol impairs ADH (antidiuretic hormone) action, reducing the kidney's ability to concentrate urine, leading to dilute urine and compensatory drinking. |
| Increased appetite (polyphagia) | 90%+ of cases | Cortisol directly stimulates appetite centers and promotes gluconeogenesis, owners often describe dogs that are suddenly ravenous despite no dietary change. |
| Pot-bellied appearance (pendulous abdomen) | ~85% of cases | Cortisol promotes fat redistribution to the abdomen and causes muscle wasting, weakening the abdominal muscles that normally hold the belly in place. |
| Symmetrical hair loss (bilateral truncal alopecia) | ~70% of cases | Cortisol disrupts the normal hair follicle cycle. Hair loss typically begins on the flanks and gradually spreads; the head and extremities are often spared. |
| Lethargy and exercise intolerance | ~65% of cases | Muscle wasting (myopathy) caused by chronic cortisol excess reduces muscle mass and strength, leading to weakness and reduced activity. |
| Skin changes (thinning, darkening, calcinosis cutis) | ~65% of cases | Cortisol thins the dermis. Calcinosis cutis, calcium deposits in the skin forming firm, chalky plaques, is a specific finding in some Cushing's dogs. |
| Panting (excessive, unprovoked) | ~60% of cases | Central effects of cortisol excess on the respiratory center, combined with abdominal pressure from the pot belly and muscle weakness. |
| Recurrent infections (skin, urinary) | ~50% of cases | Cortisol is immunosuppressive. Chronic immunosuppression predisposes to recurring bacterial skin infections (pyoderma) and urinary tract infections. |
| Neurological signs (if pituitary macroadenoma) | ~15% of PDH | Large pituitary tumors can compress the overlying brain tissue, causing disorientation, behavioral changes, circling, seizures, and blindness. |
Cushing's Disease in Cats: Different Presentation
Feline Cushing's disease presents differently from the canine form. The most striking feature in cats is extremely fragile, paper-thin skin that tears with minimal trauma, a condition called feline acquired skin fragility syndrome. Other features include pot-bellied appearance, hair loss, weight loss (despite polyphagia), and muscle wasting. Crucially, nearly all cats with Cushing's also have poorly regulated diabetes mellitus. The combination of insulin-resistant diabetes and classic skin fragility in a middle-aged cat is a strong indicator.
How Is Cushing's Disease Diagnosed?
Cushing's disease cannot be diagnosed from symptoms alone, multiple other conditions produce similar presentations. Diagnosis requires a combination of blood and urine tests, often performed in sequence:
Step 1: Screening Blood and Urine Tests
A complete blood count, biochemistry panel, and urinalysis are typically the first step. Findings suggestive of Cushing's include elevated alkaline phosphatase (ALP, often dramatically elevated), elevated cholesterol, elevated blood glucose, dilute urine (specific gravity below 1.020), and occasionally a "stress leukogram" (elevated white cell count with a specific pattern).
Step 2: Confirmatory Endocrine Testing
Two tests are commonly used. The Low-Dose Dexamethasone Suppression Test (LDDST) is the most sensitive screening test, a small dose of dexamethasone is given, and cortisol is measured 4 and 8 hours later. In normal dogs, dexamethasone suppresses cortisol production; in Cushing's dogs, suppression does not occur. The ACTH Stimulation Test is less sensitive for diagnosis but important for monitoring treatment response.
Step 3: Differentiating PDH from ADH
Once hyperadrenocorticism is confirmed, it is important to determine whether the tumor is on the pituitary (PDH) or adrenal gland (ADH), as this significantly affects treatment options. An abdominal ultrasound is the primary imaging tool, it can visualize adrenal gland size and identify adrenal tumors. A High-Dose Dexamethasone Suppression Test (HDDST) and endogenous ACTH measurement may also be used.
Cushing's Testing Requires Careful Interpretation Cushing's disease tests are prone to false positives in dogs experiencing chronic illness, stress, or receiving medications. The results must always be interpreted alongside clinical signs and by a veterinarian experienced in endocrinology. Premature or incorrect diagnosis leads to treatment of a condition the dog does not have, with serious consequences.
Treatment Options
Trilostane (Vetoryl), First-Line Medical Treatment
Trilostane is the most widely used medical treatment for canine PDH and adrenal-dependent Cushing's in many countries. It works by blocking an enzyme (3-beta-HSD) in the adrenal gland's cortisol synthesis pathway. Trilostane is given once or twice daily by mouth and requires regular monitoring (ACTH stimulation tests typically 10 days, 4 weeks, and 12 weeks after starting, then every 3–6 months). The goal is control, not cure, lifetime treatment and monitoring is required.
Mitotane (Lysodren), Alternative Medical Treatment
Mitotane selectively destroys the cortisol-producing layers of the adrenal cortex. It requires an intensive induction phase with very careful monitoring for signs of hypoadrenocorticism (Addison's disease, the opposite of Cushing's, where too little cortisol is produced). Once widely used, it has largely been replaced by trilostane in many countries but remains an option, particularly in dogs tolerating it well or in markets where trilostane is unavailable.
Surgery, For Adrenal Tumors
Surgical adrenalectomy (removal of the affected adrenal gland) is the treatment of choice for ADH caused by a unilateral adrenal tumor. Surgery carries notable risks and requires a specialist surgeon and post-operative management for adrenal insufficiency, but can be curative for benign tumors. It is not used for PDH.
Radiation Therapy, For Pituitary Macroadenomas
Dogs with large pituitary tumors causing neurological signs may be candidates for radiation therapy. It does not cure the Cushing's directly but can shrink the tumor, reducing neurological signs and in some cases improving cortisol control.
Monitoring and Long-Term Management
Dogs receiving medical treatment for Cushing's require lifelong veterinary monitoring. Owners must watch for signs of over-treatment (too little cortisol, addisonian crisis): lethargy, weakness, vomiting, diarrhea, collapse. These require emergency veterinary care. Conversely, inadequate treatment leaves the signs of Cushing's present. Successful management aims for a quality of life that is near-normal, reduced thirst and urination, improved coat, regained muscle mass, and better energy levels.
It is important to understand that Cushing's disease is not curable with medication, it is managed. Most dogs with well-controlled Cushing's live good-quality lives for several years after diagnosis, though the average survival after diagnosis is approximately 2 years when accounting for the age at diagnosis and concurrent conditions.
Keep a Symptom Diary Track your dog's daily water intake, urination frequency, appetite, energy level, and coat condition. This baseline data is invaluable for monitoring treatment response and catching early signs of over- or under-treatment between scheduled veterinary visits. Some veterinary practices provide monitoring sheets for Cushing's patients.