What Is Cushing's Disease in Dogs?
Cushing's disease, known medically as hyperadrenocorticism, is one of the most common endocrine disorders seen in middle-aged and older dogs. It occurs when the body produces excessive amounts of cortisol, a hormone manufactured by the adrenal glands. Cortisol plays a vital role in managing stress, regulating metabolism, and supporting immune function, but when levels remain chronically elevated, the effects on the body are widespread and damaging.
There are two primary forms of the disease. Pituitary-dependent Cushing's is by far the most common, accounting for around 80 to 85 per cent of cases. It occurs when a benign tumour on the pituitary gland sends out excessive signals telling the adrenal glands to produce more cortisol. The second form, adrenal-dependent Cushing's, involves a tumour on one of the adrenal glands themselves. A third, less common cause is iatrogenic Cushing's, which develops after prolonged use of corticosteroid medications.
Recognising the Symptoms
The signs of Cushing's disease tend to develop gradually, which is why many owners initially attribute them to normal ageing. Knowing what to look for can make a significant difference to how early the condition is caught.
- Increased thirst and urination, often dramatically so
- A noticeably enlarged, pot-bellied abdomen
- Increased appetite and weight gain
- Hair loss, particularly on the flanks and abdomen, without itching
- Skin that becomes thin, fragile, and prone to bruising
- Muscle weakness and reduced exercise tolerance
- Panting more than usual, even at rest
- Recurrent skin or urinary tract infections
The pot-bellied appearance results from fat redistribution and weakening of the abdominal muscles, both direct consequences of elevated cortisol. Breeds such as Poodles, Dachshunds, Beagles, and Yorkshire Terriers appear to be predisposed, though any dog can develop the condition.
How Vets Diagnose Cushing's Disease
Diagnosis requires a combination of clinical assessment, routine bloodwork, and specific hormonal testing. A standard blood panel will often reveal elevated alkaline phosphatase levels, dilute urine, and increased cholesterol, all of which point toward Cushing's as a possibility.
Your vet will then use one or more of the following tests to confirm the diagnosis.
The Low-Dose Dexamethasone Suppression Test
This is considered the gold standard for diagnosis. A small dose of dexamethasone is injected, and cortisol levels are measured before and several hours afterwards. In a healthy dog, dexamethasone suppresses cortisol production. In a dog with Cushing's, this suppression does not occur normally.
The ACTH Stimulation Test
This test measures how strongly the adrenal glands respond to stimulation by ACTH, a hormone from the pituitary gland. It is particularly useful for diagnosing iatrogenic Cushing's and for monitoring treatment response once therapy has begun.
Urine Cortisol to Creatinine Ratio
A urine sample collected at home first thing in the morning can screen for cortisol excess. It is a sensitive test but not specific, so a positive result usually prompts further investigation rather than confirming diagnosis on its own.
Once Cushing's is confirmed, abdominal ultrasound can help distinguish between pituitary and adrenal forms by visualising the adrenal glands. An MRI or CT scan may also be recommended to identify the pituitary tumour if surgery is being considered.
Treatment Options
The appropriate treatment depends on the type of Cushing's and the individual dog's health status.
Medical Management
For pituitary-dependent Cushing's, the most widely used medication in the UK is trilostane, sold under the brand name Vetoryl. Trilostane works by blocking an enzyme involved in cortisol synthesis, reducing production without destroying adrenal tissue. It requires careful dose titration and regular ACTH stimulation testing, particularly in the early months of treatment.
Mitotane is another option, though less commonly used in the UK. It selectively destroys the cortisol-producing cells of the adrenal glands and must be used with great caution due to the risk of over-suppression.
Surgical Options
Adrenal-dependent Cushing's caused by a unilateral adrenal tumour can sometimes be treated with surgical removal of the affected gland. This is a complex procedure with notable risks, and outcome depends heavily on whether the tumour has spread. In cases where surgery is successful, the prognosis can be excellent.
Long-Term Management and Monitoring
Cushing's disease is manageable rather than curable in most cases, and dogs placed on trilostane will require lifelong medication and monitoring. Regular blood tests, typically every three to six months once the dose is stable, are essential to ensure cortisol levels remain within the target range.
Owners should watch closely for signs of Addison's-like crisis, a rare but serious complication where cortisol is suppressed too aggressively. Symptoms include sudden lethargy, vomiting, loss of appetite, and weakness. This constitutes a veterinary emergency.
With appropriate treatment, many dogs with Cushing's disease go on to live comfortable, good-quality lives for several years. The key lies in consistent monitoring, prompt dose adjustments when needed, and working closely with a vet experienced in managing the condition.