Treating Pituitary Pars Intermedia Dysfunction (or Cushing's Disease)

"Many cases do fine with management changes alone," said Harold Schott, DVM, PhD, Dipl. ACVIM, professor of large animal clinical sciences at Michigan State University, at the 2006 AAEP Convention. "This might include body clipping, regular hoof care, nutrition changes (such as reducing sugars and other rich carbohydrates), and good dental care to ensure proper eating for these older horses.

"Whether a horse needs medication and when that should be started is decided on an individual basis," he added. "When a horse is put on medications, I recommend twice-annual reassessment--clinical examination and glucose/endocrine (hormone) testing. If needed, we adjust medication dosing, then retest the horse in 30-60 days to make sure his (hormone) responses are in the appropriate range."

There's also the issue of the horse that is a possible PPID case, but it's between August and November, so testing is of little value (seasonal changes can alter test results). In these cases, "if the owner can afford it, we might treat the horse for a few months just in case, then try to take him off medications and test to see if it's truly warranted," Schott commented.

For confirmed cases, "Is continuous treatment required?" he asked. "We don't really know. Epidemiological studies are hard enough, let alone following horses for 10 years (for the research needed to answer this question)."

Medication options for PPID include pergolide, cyproheptadine, trilostane, and chasteberry extract. One disadvantage is that no treatment is currently FDA-approved for PPID in horses.

Pergolide Schott described several studies that found this once daily medication to be a superior treatment in terms of improved hormone test results and owner assessment of improvement, although the latter might have also been due to improved management. Disadvantages are that it's expensive (there's a cheaper compounded product available, but you have quality and liability concerns), it causes transient inappetence in some (less than 10% of horses), and it causes lethargy (depression) in rare cases, he said.

Cyproheptadine "This medication used to be less expensive than pergolide; now it's more expensive," Schott commented. Some have suggested that it might act synergistically with pergolide, but he said there were no studies proving this. Disadvantages include limited efficacy, no pharmacological data, increasing price, and compounded product quality/liability concerns.

Trilostane This targets the adrenal gland to decrease cortisol production, so it could be used with pergolide, Schott commented. "It was shown to be effective in reversing clinical signs in one study in the United Kingdom," he added. "But adrenal cortex hyperplasia (overgrowth and overactivity) is not very common, so trilostane doesn't make sense as a front-line treatment (it doesn't address the pituitary gland dysfunction). "Also, it's not approved for use in horses, not available in the United States, and pricey," he added.

Chasteberry extract (Vitex agnus castus) Schott reported that in one field study of this product, all owners reported improved demeanor, 22 of 120 horses had improved shedding, and no horses showed changes in hormone levels. In contrast, another study presented at the 2002 AAEP convention found that 13/14 horses deteriorated on the same product.

"Another take-home message: Spend money on better management rather than questionable products," recommended Schott.



Get research and health news from the American Association of Equine Practitioners 2006 Convention in The Horse's AAEP 2006 Wrap-Up sponsored by OCD Equine. Files are available as free PDF downloads.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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