In our new age of horses as companion animals, a significant proportion of our equine population would be considered into or at least approaching the geriatric phase of life. Equine pituitary disease and disorders are a concern in the horse-owning public and what we call simply "Cushings Disease" is being studied by researchers as a complex condition or even set of conditions and/or disease.
For horse owners, the problem is always to obtain a definitive diagnosis and to understand a prognosis, if it is possible to have one. Laminitis, in subtle or complex forms, often is a side effect of pituitary disease and any progress in understanding, diagnosing and treating the disease more effectively is welcome. Here's an update from one researcher at the University of Pennsylvania.
Jill Beech VMD presented data resulting from recent research at the Dorothy Havemeyer Geriatric Workshop in Cambridge, Massachusetts, October 24-27. Dr. Beech
(show left, University of Pennsylvania photo) is the Georgia E. and Philip B. Hofmann Professor of Medicine and Reproduction at
University of Pennsylvania School of Veterinary Medicine’s
New Bolton Center in Kennett Square, PA. Her clinical and research expertise is focused on equine pituitary disease and disorders. The Dorothy Russell Havemeyer Foundation, Inc. is a private foundation that conducts scientific research to improve the general health and welfare of horses.
Dr. Beech’s research compared two different diagnostic tests, using two different hormones, to measure equine pituitary dysfunction. “First,” says Dr. Beech, “I compared measuring alpha-melanocyte stimulating hormone [MSH] with measuring adrenocorticotropic hormone [ACTH] to determine if one hormone was superior to the other in making a diagnosis. MSH is more specific for the part of the pituitary that is abnormal in horses with Cushing’s disease.”
Although both hormones are secreted from that area, ACTH is also secreted from another area in the pituitary, so it was hypothesized that MSH would be more specific and a better hormone for evaluation. Results, however, did not indicate that MSH was a more sensitive or specific indicator for pituitary dysfunction. Those data, along with the fact that ACTH, but not MSH, can be measured in diagnostic laboratories available to veterinarians has important practical application.
“This means,” says Dr. Beech, “that veterinarians can continue to measure ACTH in a reliable laboratory. At New Bolton Center, we use the laboratory at Ryan Veterinary Hospital of the University of Pennsylvania or the New York State diagnostic laboratory at Cornell.”
Data collected also indicates that when horses have high levels of these hormones, single samples can be misleading due to variability of endogenous concentrations; veterinarians should therefore obtain several basal samples for ACTH measurement.
“If basal levels of ACTH are high, it can be an indication that the horse has Pituitary Pars Intermedia Dysfunction [PPID] or Cushing’s Disease. However, some affected horses have normal basal levels, and in those cases,” says Dr. Beech, “ACTH response to a thyroid releasing hormone [TRH] test should be performed. Affected horses have an abnormal and prolonged increase in their ACTH levels compared to normal horses.”
She and her co-investigators also compared the TRH stimulation test to the domperidone stimulation test, a diagnostic test that initially appeared promising for diagnosing pituitary disease in horses. In this population of horses, the domperidone stimulation test did not appear as good as the TRH stimulation test in differentiating horses with PPID from normal horses.
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