Cushing's Disease in Dogs: Symptoms, Testing and Treatment

Cushing's disease — known medically as hyperadrenocorticism — is one of the most common endocrine disorders in dogs, yet it remains one of the most frequently missed diagnoses in veterinary medicine. At its core, Cushing's disease is a condition of excess cortisol production. Cortisol, often called the 'stress hormone,' is produced by the adrenal glands and plays vital roles in metabolism, immune function, blood pressure regulation, and the body's response to stress. In healthy dogs, cortisol production is tightly regulated by a feedback loop involving the hypothalamus, pituitary gland, and adrenal glands. In Cushing's disease, this feedback loop is disrupted, resulting in chronically elevated cortisol levels that gradually damage virtually every organ system.

"Cushing's disease is the great mimicker of veterinary medicine. Its symptoms develop so gradually and overlap with so many other conditions that owners often attribute them to normal ageing. By the time a diagnosis is made, many dogs have been symptomatic for months or even years. Awareness is the first step toward earlier detection and better outcomes." — Dr. Sarah Chen, DVM

The condition predominantly affects middle-aged to older dogs, typically presenting between eight and twelve years of age. Certain breeds are overrepresented, including Poodles, Dachshunds, Beagles, Boston Terriers, Boxers, and Yorkshire Terriers, though any breed can be affected. Small to medium breeds are more commonly diagnosed, partly because they tend to live long enough for the condition to develop and be recognised. As discussed in our senior pet care guide, endocrine disorders become increasingly common as dogs age, making regular veterinary screening essential for older pets.

Understanding the three types of Cushing's disease is essential for both diagnosis and treatment, as each type has different underlying causes, prognoses, and management approaches. The type determines whether medical management or surgery is the most appropriate path forward.

Cushing's disease in dogs falls into three distinct categories, each with a different cause and treatment approach. Identifying the type is a critical step in the diagnostic process because it directly determines the optimal management strategy.

Pituitary-dependent Cushing's (85 per cent of cases): The most common form involves a tumour — usually a benign microadenoma — in the pituitary gland at the base of the brain. This tumour produces excessive adrenocorticotropic hormone (ACTH), which in turn stimulates both adrenal glands to produce excessive cortisol. Because the tumour is driving overproduction of the stimulating hormone, both adrenal glands become enlarged (bilateral adrenomegaly). Most pituitary tumours in dogs are small (microadenomas under 10 millimetres) and grow slowly, which is why the condition develops gradually over months to years. However, approximately 10 to 15 per cent are macroadenomas — larger tumours that can eventually cause neurological symptoms as they expand and compress surrounding brain tissue.

Adrenal-dependent Cushing's (15 per cent of cases): In this form, a tumour develops directly on one of the adrenal glands, causing that gland to autonomously produce excessive cortisol independent of pituitary signalling. These tumours can be benign adenomas or malignant carcinomas — the distinction matters significantly for prognosis and treatment. Adrenal tumours produce so much cortisol that the pituitary's ACTH production is suppressed via negative feedback, causing the opposite (non-tumorous) adrenal gland to shrink (atrophy). Abdominal ultrasound is particularly useful for distinguishing adrenal-dependent from pituitary-dependent Cushing's, as it can visualise adrenal gland size and symmetry.

Iatrogenic Cushing's: This form is not a disease per se but a side effect of long-term corticosteroid medication. Dogs receiving prednisone, prednisolone, dexamethasone, or other glucocorticoids for conditions like allergies, immune-mediated diseases, or inflammatory conditions can develop all the symptoms of Cushing's disease due to the exogenous cortisol. The treatment is gradual tapering of the steroid medication under veterinary supervision — abrupt discontinuation can cause a life-threatening Addisonian crisis as the suppressed adrenal glands cannot immediately resume normal cortisol production.

Why type matters: Pituitary-dependent Cushing's is typically managed medically with trilostane (Vetoryl), while adrenal tumours may be candidates for surgical removal — especially benign adenomas, which can be curative. Iatrogenic Cushing's requires a careful medication review. Distinguishing between these types requires specific diagnostic tests and imaging, which is why the diagnostic workup for Cushing's can be both complex and costly.

The symptoms of Cushing's disease develop gradually — often so slowly that owners accommodate each change without realising they form part of a larger pattern. Recognising these signs, even individually, should prompt a conversation with your veterinarian, particularly in middle-aged to older dogs.

Excessive thirst and urination (polydipsia/polyuria): This is often the first symptom owners notice and the most disruptive. Cortisol interferes with the action of antidiuretic hormone (ADH), causing the kidneys to produce large volumes of dilute urine. Dogs may drink two to ten times their normal water intake and need to urinate far more frequently — often having accidents in the house, even if previously perfectly housetrained. Many owners initially attribute this to a urinary tract infection or simply 'getting old.'

Pot-bellied appearance: One of the most visually distinctive signs of Cushing's is the development of a pendulous, pot-bellied abdomen. This results from a combination of factors: cortisol causes redistribution of body fat to the abdominal area, weakens the abdominal muscles, and enlarges the liver (hepatomegaly). The result is a dog that looks increasingly barrel-shaped despite sometimes eating the same amount — or even losing weight elsewhere on the body.

Skin and coat changes: Cortisol has profound effects on the skin. Hair loss (alopecia) is common, typically occurring symmetrically on both sides of the body while sparing the head and legs. The skin becomes noticeably thin and fragile — you may be able to see blood vessels through it. Hyperpigmentation (darkening of the skin), comedones (blackheads), and calcinosis cutis (calcium deposits in the skin that appear as hard, white plaques) can all develop. Recurrent skin infections, poor wound healing, and easy bruising are also characteristic.

Other common symptoms: Excessive panting — even at rest and in cool environments — affects approximately 30 to 40 per cent of Cushingoid dogs. Increased appetite (polyphagia) is common and can be dramatic — dogs may become food-obsessed, stealing food or raiding bins. Muscle weakness and wasting, particularly of the limbs, creates the characteristic combination of thin legs supporting a pot belly. Lethargy and exercise intolerance develop as the disease progresses. Recurrent urinary tract infections are common due to cortisol's immunosuppressive effects. Our veterinary visit guide explains why regular check-ups become increasingly important as your dog ages and these symptoms may emerge.

Diagnosing Cushing's disease is notoriously complex. There is no single perfect test, and results must be interpreted in the context of clinical signs, history, and other laboratory findings. Your veterinarian may use one or more of the following tests, often in combination, to build a diagnostic picture.

Low-dose dexamethasone suppression test (LDDS): Considered the screening test of choice by many veterinary endocrinologists, the LDDS test measures the body's cortisol response to a small dose of synthetic cortisol (dexamethasone). In healthy dogs, the exogenous dexamethasone signals the pituitary to reduce ACTH production, causing cortisol levels to drop. In dogs with Cushing's, cortisol remains stubbornly elevated because the feedback loop is disrupted. The test requires blood samples at baseline, four hours, and eight hours after the dexamethasone injection. It has a sensitivity of approximately 85 to 95 per cent for Cushing's disease but can produce false positives in dogs with other illnesses — the so-called 'stress' response to non-adrenal illness.

ACTH stimulation test: This test measures the adrenal glands' response to synthetic ACTH (Cortrosyn). A baseline blood sample is taken, synthetic ACTH is injected, and a second sample is drawn one hour later. Dogs with Cushing's typically show an exaggerated cortisol response — their already-overstimulated adrenal glands respond dramatically to the additional ACTH. The ACTH stimulation test is simpler and faster than the LDDS test but is less sensitive (approximately 60 to 85 per cent). It is, however, the only test that can diagnose iatrogenic Cushing's and is the standard monitoring test used to adjust trilostane dosing once treatment begins.

Urine cortisol:creatinine ratio (UCCR): This is a useful screening test that can be performed on a urine sample collected at home — ideally a morning sample. The UCCR reflects cortisol production over several hours, averaging out the natural fluctuations in cortisol that occur throughout the day. A normal UCCR effectively rules out Cushing's disease (high negative predictive value), but an elevated UCCR does not confirm it — many other conditions and even stress can elevate the ratio. It is best used as a first-line screening tool: if normal, Cushing's is very unlikely; if elevated, further testing with LDDS or ACTH stimulation is needed.

Imaging: Abdominal ultrasound is invaluable for evaluating adrenal gland size and shape, identifying adrenal tumours, and assessing liver size. Advanced imaging — CT or MRI of the brain — may be recommended if a pituitary macroadenoma is suspected, particularly if neurological symptoms are present or radiation therapy is being considered.

The treatment of Cushing's disease depends on the type, the severity of symptoms, and the overall health of the patient. For most dogs with pituitary-dependent Cushing's, medical management is the standard approach, while adrenal tumours may be candidates for surgical removal.

Trilostane (Vetoryl): Trilostane is the first-line medical treatment for both pituitary-dependent and inoperable adrenal-dependent Cushing's disease. It works by inhibiting an enzyme (3-beta-hydroxysteroid dehydrogenase) in the adrenal glands that is essential for cortisol production. Trilostane does not cure Cushing's — it controls it by reducing cortisol output. Treatment is lifelong, typically given once or twice daily with food (food significantly improves absorption). The starting dose is based on body weight, and careful monitoring with ACTH stimulation tests is required — usually at 10 days, 4 weeks, and 12 weeks after starting, then every 3 to 6 months thereafter. Dose adjustments are common in the first few months as the optimal level is determined.

Monitoring on trilostane: Regular ACTH stimulation tests are essential to ensure the cortisol level is adequately suppressed without being driven too low. Over-suppression can cause iatrogenic hypoadrenocorticism (Addison's disease) — a potentially life-threatening drop in cortisol and sometimes aldosterone. Signs of over-suppression include lethargy, loss of appetite, vomiting, diarrhoea, weakness, and collapse. If you see these signs, stop trilostane and contact your vet immediately. Most dogs improve dramatically on trilostane — excessive thirst and urination often reduce within the first two weeks, and skin and coat improvements follow over two to six months.

Surgery for adrenal tumours: Adrenalectomy — surgical removal of the affected adrenal gland — can be curative for adrenal-dependent Cushing's, particularly for benign adenomas. However, adrenal surgery is technically demanding due to the glands' proximity to major blood vessels (the vena cava and aorta), and should only be performed by experienced veterinary surgeons. Perioperative complications include haemorrhage, thromboembolism, and temporary or permanent hypoadrenocorticism as the atrophied opposite gland recovers function. Despite these risks, successful adrenalectomy offers the possibility of a complete cure.

Radiation therapy for pituitary tumours: For dogs with pituitary macroadenomas causing neurological symptoms, radiation therapy can shrink the tumour and improve both neurological signs and cortisol control. It is typically used in combination with trilostane and is available at veterinary referral centres with radiation oncology facilities.

A Cushing's disease diagnosis is life-changing, but it is not a death sentence. With appropriate treatment and diligent monitoring, most dogs with Cushing's disease can enjoy good quality of life for years after diagnosis. Understanding what to expect and how to manage the condition day-to-day empowers you to be the best advocate for your dog's health.

Realistic expectations: Trilostane controls Cushing's disease — it does not eliminate it. Some symptoms resolve quickly (excessive thirst and urination often improve within weeks), while others take months (skin and coat changes may need three to six months to show significant improvement). Some changes, particularly muscle wasting and calcinosis cutis, may only partially reverse. Setting realistic expectations with your veterinarian helps you track progress without becoming discouraged by the speed of recovery.

Monitoring at home: Between veterinary visits, you are your dog's primary health monitor. Track water intake daily — a sudden increase may indicate the trilostane dose needs adjustment. Monitor appetite, energy levels, and urination frequency. Keep a simple log that you can share with your vet at each check-up. Watch for signs of cortisol dropping too low: lethargy, loss of appetite, vomiting, diarrhoea, or weakness — these require urgent veterinary attention.

Concurrent conditions: Cushing's disease increases the risk of several other conditions that may need simultaneous management. Hypertension (high blood pressure) affects up to 80 per cent of Cushingoid dogs and can damage the eyes, kidneys, heart, and brain. Diabetes mellitus can develop alongside Cushing's — our diabetes management guide covers this overlap. Urinary tract infections are common due to cortisol's immunosuppressive effects and the dilute urine that provides a favourable environment for bacterial growth. Protein-losing nephropathy and blood clot formation (thromboembolism) are also recognised complications.

Financial planning: Cushing's disease is an expensive condition to manage long-term. Trilostane medication, regular ACTH stimulation tests, blood panels, urine cultures, and blood pressure monitoring add up. Discuss the expected costs with your veterinarian upfront so you can plan accordingly. Pet insurance that covers chronic conditions can be invaluable — though pre-existing condition exclusions mean insurance is most valuable when obtained before symptoms develop.

When to reassess: If your dog's symptoms are not improving despite treatment, if new symptoms develop, or if quality of life is declining, it is time for a thorough reassessment. This may include retesting to confirm the diagnosis, imaging to evaluate tumour progression, or adjusting the treatment approach. Cushing's disease management is a partnership between you and your veterinary team — open communication and regular monitoring are the keys to the best possible outcome for your dog.