Hypoadrenocorticism, also called Addison's disease, is an endocrine disorder that results from a deficient production of adrenal gland hormones. There are two adrenal glands in the abdomen that lie just in front of the kidneys.

Hypoadrenocorticism is very rare in the cat, but the most common cause is destruction of the adrenal gland tissue by the animal's immune system. Infrequently, certain infections, infiltration of the adrenal glands with lymphosarcoma, and diseases of the pituitary gland may also cause Addison's disease.

Occasionally Addison's disease is caused by the abrupt discontinuation of steroid medication. Cats that have been on long-term steroids should be slowly weaned off such drugs in order to avoid this form of hypoadrenocorticism.

Although Addison's is extremely rare in cats, it affects primarily young cats. Any breed or sex may be affected.

In hypoadrenocorticism there is usually a deficiency of two different groups of hormones, the glucocorticoids and the mineralocorticoids. The primary glucocorticoid hormone is cortisol, and it is responsible for combating stress, helping to maintain blood sugar. The major mineralocorticoid is aldosterone. Aldosterone regulates the water, sodium, potassium, and chloride concentrations in the body. Most naturally occurring forms of Addison's disease affects both hormones. Addison's disease secondary to the abrupt withdrawal of steroid medications affects only the level of circulating cortisol.

What to Watch For

The clinical signs seen with Addison's disease are often very vague in the cat. They mimic many other diseases, so a high degree of suspicion must be present for the disease to be recognized. With an acute crisis, the signs are more pronounced and profound. Clinical signs include:

Lethargy, weakness

Poor appetite

Weight loss

Dehydration

Vomiting

Excessive thirst (polydipsia) and urination (polyuria)

Low body temperature, shaking, collapse, low heart rate

Diagnosis

Because hypoadrenocorticism can mimic many other diseases, diagnostic tests are needed to confirm the presence of Addison's disease, and to exclude other diseases that cause similar signs. These tests may include:

Complete medical history and physical examination

A complete blood count (CBC), blood biochemistry profile and urinalysis

An ACTH stimulation test (the diagnostic test of choice)

Chest and abdominal radiographs (X-rays) and possible abdominal ultrasound, depending on the clinical symptoms

Treatment

Treatment depends on whether the onset of illness is acute with severe symptoms, or whether more mild, chronic signs are present. For acute disease (an Addisonian crisis) treatment may include:

Intravenous fluid therapy

Electrolyte and acid-base monitoring

Corticosteroid and mineralocorticoid replacement therapy

Treatment for chronic disease may include:

Corticosteroid and mineralocorticoid replacement therapy

Daily salt supplementation

Home Care

At home, administer any prescribed medication precisely as directed by your veterinarian. Observe the cat's activity level, appetite and water intake. Also, report any occurrence of vomiting, diarrhea, weakness, and change in appetite to your veterinarian immediately. Regularly scheduled veterinary visits are needed to monitor the disease and response to treatment. Such exams often involve various tests to monitor the levels of sodium and potassium in the blood.

Some cats have different medication needs during times of stress such as travel, surgery, or hospitalization. Be sure to discuss this with your veterinarian if you anticipate times of stress in the future.

Preventative Care

There is no preventative measure for the naturally occurring forms of this disease. If your cat is receiving steroid medication, do not stop the medication abruptly. By doing so, an Addisonian crisis can occur. This is the only form of Addison's disease that is preventable.