Hyperadrenocorticism (Cushing's syndrome)
Hyperadrenocorticism, also known as Cushing's syndrome, is a common endocrine disorder in dogs. The clinical signs are caused by an excess of cortisol (the body's form of cortisone). This occurs because of increased secretion of cortisol by the adrenal glands in response to an abnormality in the pituitary gland in the brain, or because of a tumour in the adrenal glands themselves. Cushing's syndrome is more common in certain breeds, usually in dogs that are 6 years of age or older.
Hyperadrenocorticism may also occur in any dog that is being treated with excessive amounts of glucocorticoids. Glucocorticoid medication, often called steroids, is an important part of therapy in many different conditions in dogs.
Cortisol affects many body functions including the metabolism of protein, carbohydrate and fat, the immune response, and the inflammatory response. Because of this, there are a wide variety of signs which may be associated with this disorder. Hyperadrenocorticism is insidious in onset and progresses slowly.
Usually the first signs are a gradual increase in appetite, drinking and urination. These changes may be overlooked until other abnormalities are noticed such as symmetrical hair loss over the trunk of the body, thinning skin, muscle wasting, a pendulous abdomen, panting, and an inflammatory skin condition called calcinosis cutis. Poor wound healing and an increased susceptibility to skin infections are also common.
Diagnosis is based on typical clinical signs as described above, laboratory abnormalities, and adrenal function tests which will help your veterinarian to determine if the disease is caused by abnormal pituitary stimulation of the adrenal glands, or by an adrenal tumour.
If an adrenal tumour can be identified, it may be possible to remove it surgically, depending on the location and size of the tumour and whether it is benign or malignant.
For hyperadrenocorticism due to pituitary disease, or for inoperable adrenocortical tumours, medical treatment is used. There are several effective drugs available to decrease the production of cortisol by destroying part of the adrenal gland or by blocking synthesis. Your veterinarian will tell you what to expect with the use of these drugs and will monitor your dog's response to treatment carefully. Improvement in some clinical signs (more normal appetite and water intake) occurs quickly; reversal of skin and hair coat changes often takes 3 to 6 months; clinical pathological changes (elevations in liver enzymes for example) may take even longer to resolve.
- CLINICAL PATHOLOGY: There are a wide variety of abnormalities seen that are consistent with hyperadrenocorticism. Concurrent medical problems, secondary to Cushing's disease, may also be identified.
- ULTRASONOGRAPHY: A skilled radiologist can usually visualize the adrenal glands to evaluate the size and shape, and, if an adrenal mass is seen, can screen for hepatic or other organ metastasis
- DISCRIMINATION TESTS: ACTH stimulation test, low-dose dexamethasone test, high-dose dexamethasone suppression test - these tests can be used to discriminate between pituitary dependent and adrenocortical tumour hyperadrenocorticism [see reference below for detailed discussion]
Since little is known about the inheritance of this condition, the best advice for prevention is to select breeding dogs from families with no history of the disorder.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
Feldman, E.C. 1995. Hyperadrenocorticism. In S.J. Ettinger and E.C. Feldman (eds.) Textbook of Veterinary Internal Medicine p. 1538-1578. W.B. Saunders Co., Toronto.