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Definitive Diagnosis Can Be Difficult in Cushing'sDisease

Pet Column for the week of August 10, 1998

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Services - Dermatology

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
By Sarah Probst
Information Specialist

Pot belly, lethargy, vomiting, diarrhea, urinating more often, eating and drinking more, and
losing hair uniformly on both sides of the body. One or all of these symptoms can cause
veterinarians to suspect a hormonal imbalance known as Cushing's disease; however, none
of these symptoms can confirm it. Cushing's disease-also known as
hyperadrenocorticism-can occur in many species, including humans. It is most prevalent in
middle-aged to older dogs, especially poodles, dachshunds, Boston terriers, and boxers. A
variety of tests pinpoint whether Cushing's disease is present and what is causing the
hormonal imbalance, but none of these tests is infallible.

Dr. Charles Wiedmeyer, a veterinarian formerly at the University of
Illinois College of Veterinary Medicine, conducted research on improving the diagnostic
capabilities of veterinarians. "Initially, you can look at an animal and suspect Cushing's
disease, but obtaining a definitive diagnoses can be a challenge. My goal is to determine
how cortisol-a natural steroid hormone secreted by the adrenal glands-affects a specific
enzyme so we can improve our diagnostic abilities using that enzyme."

An increase in cortisol secreted by the adrenal glands causes Cushing's disease; however,
the adrenal glands are not always the gland malfunctioning. The adrenal gland receives
signals, in the form of a hormone called ACTH, from the pituitary gland. ACTH tells the
adrenal gland it is time to secrete cortisol. Once the appropriate amount of cortisol is
circulating, sensors inform the pituitary gland that enough ACTH has been secreted. Then,
the pituitary gland decreases ACTH secretion and the adrenal glands decrease the amount
of cortisol being secreted. Thus Cushing's disease can be caused by a pituitary malfunction,
an adrenal malfunction, or by human intervention.

"Eight-five percent of cases are pituitary-dependent Cushing's," says Dr. Wiedmeyer. "It is
difficult to treat pituitary dependent Cushing's disease because the pituitary gland is hard to
get to. Veterinarians will treat with Mitotane or o,p'-DDD--a derivative of the insecticide
DDT. You have to monitor the disease very closely because you are wiping out part of the
adrenal gland in the process," says Dr. Wiedmeyer. "These treatments selectively kill cells in
the adrenal gland that are producing cortisol." Even though the pituitary gland is still
producing excess ACTH, the adrenal gland won't have as many cells to produce cortisol;
cortisol levels will decrease to a more normal level.

"If an adrenal tumor is causing the additional secretion of cortisol, you can go in and remove
the tumor," explains Dr. Wiedmeyer. With removal of all or part of the adrenal glands,
supplemental cortisol must be followed conscientiously. "Administration of cortisol is a
lifelong process," explains Dr. Wiedmeyer.

Cushing's disease can also be induced by a veterinarian. Prednisone, a synthetic steroid, is
often used to treat skin disorders and as an anti-inflammatory agent. Steroids act like
natural cortisol. Long term use of steroids eliminates the need for cortisol production by the
adrenal gland. With decreased function, the adrenal glands shrink in size. Slow withdrawal
of steroids is normal treatment. Eliminating steroids abruptly can have fatal consequences.

The variety of clinical signs makes Cushing's disease difficult to diagnose without further
testing. Veterinarians in clinical pathology like Dr. Wiedmeyer strive to make this process
easier, "We deal with diagnostic techniques every day. Our service at the college for
veterinarians is to help them make diagnoses more easily and accurately."