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Hyperadrenocorticism PDF Print E-mail

Cushing's Disease is a disorder caused by excessive production of cortisol by the adrenal gland. Corticosteroid drugs such as prednisone, dexamethasone, and cortisone are closely related to and have similar actions to the body's natural cortisol. Clinical signs are due to the deleterious effects of the elevated circulating cortisol concentrations on multiple organ systems.  

  • 85% of cases are caused by pituitary tumors (usually benign)
  • 15% of cases are caused by adrenal tumors (half malignant, half benign).
Signs may include excessive drinking, urination and increased appetite, potbelly, enlarged liver, hair loss, lethargy, muscle weakness, obesity, muscle atrophy, increased panting, loss of estrus cycle, testicular atrophy, increased pigment of areas of skin, calcium deposits in skin and other organs, facial nerve palsy. Severity of symptoms may vary greatly, depending on the duration and severity of cortisol excess. In some cases, the physical presence of the tumor (pituitary or adrenal) contributes.

  •   Blood chemistry may show elevated alkaline phosphatase, liver enzymes, cholesterol, and glucose.
  • Urinalysis may reveal decreased specific gravity, increased protein, blood, white blood cells, or bacteria.

Diagnosing Cushing's:

  1. ACTH response test: Draw resting blood cortisol level, give ACTH injection, draw second blood cortisol level in one hour.
  2.  Low-dose dexamethasone suppression test
  3. Urine cortisol:creatinine ratio (negative result virtually excludes Cushing's Disease; a positive result must be confirmed with above blood test)


Surgery is probably the treatment of choice for adrenal tumors unless the patient is a poor surgical risk or the client refuses surgery. Medical control of adrenal-dependent Cushing's is recommended prior to surgery, if possible.


  1. Mitotane (o,p'-DDD) remains the drug of choice for medical management of Cushing's disease in dogs. In case of adverse reaction to mitotane (lethargy, weakness, anorexia, vomiting, or diarrhea) discontinue drug, give prednisone, and reevaluate in next few days. If no response to prednisone in a few hours, evaluate immediately.
  2. Give an initial loading dose until ACTH response tests are normal; then twice/week dosing. Adjustments are based on ACTH response testing. If relapse occurs, reload for 5–7 days and increase weekly maintenance dose by approximately 50%. Lifelong therapy required. Retest ACTH response test every 6 to 12 months.
  3.  L-Deprenyl (selegiline, Anipryl, Deprenyl) May be useful for pituitary dependent Cushing's disease. Low incidence of side effects.


Untreated Cushing's disease—generally a progressive disorder with a poor prognosis. Treated pituitary dependent—usually a good prognosis; the average survival time for a dog treated with mitotane is 2 years; at least 10% survive 4 years; dogs living longer than 6 months tend to die of causes unrelated to Cushing's disease. Pituitary dependent with neurologic signs—poor to grave prognosis. Benign adrenal tumors—usually a good to excellent prognosis; small malignant tumors (not metastasized) have a fair to good prognosis. Large malignant tumors and malignant tumors with widespread metastasis—generally a poor to fair prognosis, but impressive responses to high doses of mitotane are occasionally seen.