Diseases of the adrenal cortex of dogs and cats.

The most common cause of hypoadrenocorticism in dogs is idiopathic immune-mediated destruction of the adrenal cortex. Other causes include anterior pituitary insufficiency, pituitary or adrenal neoplasia, acute withdrawal of exogenous corticosteroids, and mitotane toxicity. Females are affected more often than males; only 1 feline case has been documented. Animals 2-5 years old are most commonly affected. Clinical signs include lethargy, weakness, weight loss, anorexia, vomiting, diarrhea and bradycardia. Hematologic and biochemical changes can include eosinophilia, lymphocytosis, anemia, hyperkalemia, hyponatremia and hypercalcemia. Diagnosis is by finding negligible resting levels of plasma cortisol and no response to ACTH administration, and a serum Na:K ratio of 20:1 or less. Treatment involves restoring fluid volume, correcting acidosis, and supplementing salt and glucocorticoids. Daily oral use of prednisone at 0.05 mg/kg can safely maintain most affected dogs. Some dogs only require glucocorticoids in stressful situations. Iatrogenic secondary adrenocortical insufficiency (iatrogenic Cushing's disease) may result from a single injection of long-acting glucocorticoids or from long-term use. Clinical signs are the same as for natural hyperadrenocorticism, but endogenous cortisol release is suppressed. Treatment is gradual withdrawal of the offending glucocorticoid and elimination of the cause that initially prompted glucocorticoid therapy.