Cushing Disease

Cushing’s Disease (hyperadrenocorticism) is a very common disorder in older dogs, and is often mistaken for the ageing process itself. Caused by the harmful effects of raised levels of cortisol (a corticosteroid hormone) on a dog’s organs, it results in weight gain, hair loss, a loss of bladder control and skin disorders.

Increased thirst, more urination, a large and sometimes sagging abdomen – caused by an enlarged liver and loss of muscle tone in the abdominal muscles, an increased appetite, causing weight gain, muscle atrophy and weakness, excessive panting,hair loss, skin abnormalities such as thin skin, blackheads (comedones), hyperpigmentation, calcinosis cutis (lumps of mineral-like material in the skin). Males not desexed may get atrophy of the testicles, while undesexed females will fail to cycle.

There may be a number of factors, although 85-90% of naturally-occurring cases are due to pituitary-dependent hyperadrenocorticism, where excess secretions of ACTH (adrenocorticotrophic hormone) stimulate the adrenal glands to release cortisol. In 10-15% of naturally-occurring cases tumours (malignant or benign) are present on the adrenal glands that secrete cortisol. Excessive administration of corticosteroid-containing medications can also be a cause.

Treatment is dictated by the severity of the clinical signs, the dog’s general state of health, and also the cause of the excess cortisol. For pituitary-dependent Cushing’s disease, oral medication is commonly administered to the dog to inhibit the function of the adrenal gland in producing and releasing cortisol. Regular blood tests every few months are required to monitor response to the medication. The medication will be required for life.

If an adrenal tumour is the cause, medication may be used, but surgery can also be performed to remove the tumour. If excess corticosteroid administration is the cause, tapering down and possibly off the corticosteroid drug should resolve the condition. In all cases, additional supportive therapies may be required.

Depending on the cause, severity and treatment, clinical signs may resolve themselves within days, or take up to several months after the commencement of treatment. If left untreated, Cushing’s Disease is progressive and has a poor prognosis. If controlled well on medication, the dog’s prospects are good. However for dogs with advanced tumours, especially if they are causing neurological symptoms and there are metastases (spread of the tumour to other parts of the body) the prognosis is usually bleak.