Researchers Evaluate Steps for Diagnosing Cushing’s Disease

A team of researchers recently determined what they believe to be the ideal first step for diagnosing PPID
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An earlier diagnosis for a horse often means a better prognosis for his recovery, but the reality with equine Cushing’s disease has been that clinical signs are abundant before the diagnostic process begins. A team of researchers recently determined what they believe to be the ideal first step for diagnosing PPID early, however, and this could allow affected horses to receive treatment sooner and slow the progression of the debilitating disease.

The disease is caused by an enlargement of the pars intermedia of the pituitary gland, which is the central part of the pituitary gland located at the base of the brain. When the gland becomes enlarged, it secretes excessive amounts of adrenocorticotropin hormone (ACTH) which increases adrenal gland cortisol (stress hormone) secretion. A common condition in older horses, clinical signs include a long hair coat, delayed shedding of the winter hair coat, loss of muscle mass, increased drinking and urination, a pot-bellied appearance, and an increased susceptibility to infections. If left untreated, Cushing’s horses generally experience chronic bouts of disease, a decline in health and comfort, and reduced quality of life.

There are several tests currently available to aid veterinarians in diagnosing PPID, measuring:

  • Resting adrenocorticotropic hormone levels (and keeping in mind that ACTH concentrations can be variable in an individual horse with pituitary dysfunction, it is important to get at least two blood samples);
  • Suppression of cortisol from dexamethasone administration (the dexamethasone suppression test); and
  • The change in ACTH concentrations in the blood after administering thyrotropin-releasing hormone (the TRH response test) to the horse.

However, veterinarians report that alternative tests for equine Cushing’s are needed, particularly to diagnose the disease prior to the onset of potentially life-threatening conditions, such as laminitis. In an attempt to find a better PPID diagnostic method, Jill Beech, VMD, Dipl. ACVIM, of the Department of Clinical Studies at the New Bolton Center in Pennsylvania, and colleagues compared the ACTH responses in the TRH test to those in a domperidone response test. (Domperidone is the substance that stilumates secretion of ACTH

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Written by:

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she’s worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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