Cushing's Disease in Dogs

Cushing's disease — known clinically as hyperadrenocorticism — is one of the more common hormonal disorders we see in older dogs. It develops when the body is exposed to too much cortisol over a long period. Because the changes come on slowly and look a great deal like ordinary ageing, many dogs are well into the disease before anyone suspects a problem.

What is Cushing's disease?

Cortisol is the body's stress hormone. It is produced by the adrenal glands, which sit just in front of the kidneys, and it does necessary work — regulating metabolism, blood sugar, and the immune response. Production is directed by the pituitary gland at the base of the brain, which releases adrenocorticotrophic hormone (ACTH) to tell the adrenals how much cortisol to make.

In a dog with Cushing's, that control loop breaks down and cortisol stays elevated. Useful in short bursts, sustained high cortisol gradually thins the skin, wastes muscle, and suppresses the immune system.

Symptoms to watch for

The earliest sign owners usually notice is a marked increase in thirst, and with it far more frequent urination — sometimes accidents in a previously house-trained dog. A strong increase in appetite is common too.

As the disease progresses you may see a pot-bellied appearance, loss of muscle over the back and hind legs, general weakness, and reduced stamina. Skin changes are characteristic: symmetrical hair loss over the flanks and trunk, skin that becomes noticeably thin, slow healing, and repeat skin or urinary infections. Excessive panting and restlessness, particularly at night, are also frequently reported.

These signs typically develop over a year or more. Because lower energy, a thickening waistline, and a thinning coat all read as "getting old," the disease is often well advanced before it is investigated — which is exactly why it is worth mentioning changes in thirst and urination to us early.

What causes it

Roughly eight to nine cases in ten are pituitary-dependent: a small, usually benign tumour in the pituitary gland drives the adrenals to overproduce cortisol. Most of the remainder are adrenal-dependent, caused by a tumour on an adrenal gland itself.

A third form is iatrogenic — caused by treatment rather than disease. Long courses of steroids such as prednisone or dexamethasone can produce identical signs, and so can chronic use of steroid-containing ear or skin medications, which are absorbed through the skin. This form generally resolves once the steroid is tapered off, and it should never be stopped abruptly or without veterinary guidance.

Cushing's is largely a disease of middle-aged and older dogs. Poodles, Dachshunds, Boston Terriers, Boxers, Beagles, and Yorkshire Terriers are reported to be at higher risk.

How it is diagnosed

There is no single quick test. Diagnosis starts with routine bloodwork and a urinalysis — a raised alkaline phosphatase (ALP) alongside dilute urine is a common early clue, though neither confirms anything on its own.

From there we use a dedicated hormone test. An ACTH stimulation test measures cortisol before and after an injection of ACTH; a low-dose dexamethasone suppression test instead checks whether a steroid dose suppresses cortisol as it should in a healthy dog. Abdominal ultrasound is often used alongside these to look at the adrenal glands and help distinguish the pituitary-dependent form from an adrenal tumour — a distinction that changes the treatment plan.

Testing is involved and not inexpensive, and mild cases can be genuinely ambiguous. We will talk through what each step will and will not tell you before proceeding.

Treatment

Most dogs with the pituitary-dependent form are managed with daily oral medication rather than surgery. Trilostane (Vetoryl) is the treatment used most often; mitotane (Lysodren) is an older alternative. Both work by reducing cortisol production, and both require ongoing monitoring — periodic recheck testing to keep cortisol in the right range, since too much suppression causes its own problems.

Adrenal tumours are a different situation and may be treated surgically. Surgery can be curative for a benign tumour, but it is a demanding procedure and a proportion of these tumours are malignant, so the decision depends on imaging and on your dog's overall health.

Owners usually notice drinking and urination settling within the first couple of weeks. Coat and skin changes take considerably longer — often several months — to improve.

Outlook

Cushing's is managed rather than cured, and with consistent treatment and monitoring most dogs do well and stay comfortable. Reported median survival after diagnosis is around two years, but that figure needs context: this is overwhelmingly a disease of older dogs, and most affected dogs ultimately die of unrelated age-related causes rather than of Cushing's itself.

This page is general educational information and is not a substitute for examining your pet. If your dog is showing these signs, please book an appointment so we can assess them properly. Further reading: the Merck Veterinary Manual, Cornell Riney Canine Health Center, and the American Kennel Club.