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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.

What Causes The High Levels of Cortisol?

There may be a number of factors:

  • There could be a growth on the pituitary gland in the base of the brain that causes excess secretions of ACTH (i.e. adrenocorticotrophic hormone) that in turn stimulate the adrenal glands, which are small glands near the kidneys, to release cortisol. 85-90% of naturally-occurring cases are due to this pituitary-dependent hyperadrenocorticism.
  • There could be tumours (malignant or benign) on the adrenal glands that secrete cortisol. 10-15% of naturally-occurring cases are caused by these adrenal gland tumours.
  • Excessive administration of corticosteroid-containing medications can also be a cause.
  • A large and sometimes sagging abdomen – caused by an enlarged liver and loss of muscle tone in the abdominal muscles.
  • An increased appetite. This can cause weight gain, and combined with an enlarged abdomen, can make a dog look obese.
  • Hair loss
  • Muscle atrophy and weakness
  • Excessive panting
  • Skin abnormalities such as thin skin, blackheads (comedones), hyperpigmentation, calcinosis cutis (lumps of mineral-like material in the skin)
  • Males not neutered may get atrophy of the testicles, while intact females will fail to cycle.

How Is Cushing's Disease Diagnosed?

Your veterinarian will conduct a number of tests to diagnose Cushing's Disease and to work out its cause. The tests may include urine tests and several types of blood tests, some of which may require your dog to stay at the veterinary clinic for the day. Imaging may also be done: x-rays, ultrasound and even CT scans or MRIs.

How Is Cushing's Disease Treated?

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.

What Is Expected Course And Prognosis If My Dog Is Diagnosed With Cushing's Disease?

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.

Additional Information

The Merck Veterinary Manual
Hyperadrenocorticism: Cushing's Disease

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