Could MRI Help Identify Early-Stage PPID?

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Could MRI Help Identify Early-Stage PPID?

Schott noted that while the team "pursued the project more for validation of MRI as a tool to classify research subjects … it could be used as an earlier diagnostic tool for owners willing to pursue the expense of MRI under general anesthesia."

Photo: Anne M. Eberhardt

Veterinarians have no problem diagnosing advanced pituitary pars intermedia dysfunction (PPID, or equine Cushing's disease)—the abnormally long hair coat that fails to shed (termed hypertrichosis) is about as telltale as clinical signs come in equine medicine. Confirming early stage PPID is decidedly more difficult, however, due to the subtle and vague signs it produces. Thus, researchers are continually working to identify new ways to both confirm early stage PPID and accurately classify research subjects.

At the 2014 American College of Veterinary Internal Medicine Forum, held June 4-7 in Nashville, Tennessee, Hal Schott II, DVM, PhD, Dipl. ACVIM, presented a poster detailing one of the new techniques researchers are exploring for PPID diagnosis: MRI.

A disease that affects all breeds and types of horses, PPID is caused by an enlargement of the pars intermedia in the pituitary gland, which is located at the base of the brain; essentially, as the pars intermedia enlarges, the horse's clinical signs become more severe. This disorder occurs commonly in older horses, and the frequency of diagnosis generally increases with age. However, veterinarians have recognized PPID in some younger horses, as well.

Previously, Schott and colleagues showed that another form of imaging—computed tomography (CT scanning)—allowed veterinarians to visualize pituitary gland enlargement in PPID-affected horses; however, CT scanning was not able to provide details about the pars intermedia or anything else located within the pituitary gland.

Based on clinical experience with MRI and PPID, Schott and colleagues hypothesized that MRI would yield pituitary gland and pars intermedia measurements that would correlate with post-mortem measurements. To test their hypothesis, the team employed 21 horses:

  • Seven horses with a mean age of 27 years that had PPID and were previously treated with pergolide;
  • Six horses with a mean age of 24 years that had PPID but did not receive treatment;
  • Four horses with a mean age of 25 years that did not have PPID (aged controls); and
  • Four horses with a mean age of 5 years that did not have PPID (young controls).

Each horse underwent an MRI examination immediately prior to euthanasia. The researchers (including three internal medicine clinicians and one radiologist) then evaluated the horses' pituitary glands and pars intermedia, and scored the degree of pituitary gland and pars intermedia changes visible on the MR images on a 5-point scale, with 1 being no apparent change and 5 being the most severe changes.

The team found that MRI provided great contrast and detail of the pituitary gland. Additionally, the post-mortem and MRI pituitary gland measurements were highly correlated, as were the pars intermedia/pituitary gland ratios (or the amount of the pituitary gland the pars intermedia fills). The team found that all four investigators' MRI scores were "fair" in agreement, and the agreement was "good" among the three medicine clinicians, Schott said.

The team scored the degree of pituitary gland and pars intermedia changes visible on the MR images on a 5-point scale, with 1 being no apparent change and 5 being the most severe changes.

Photo: Courtesy Dr. Hal Schott

Schott and colleagues concluded that MRI can effectively show pituitary gland and pars intermedia size, as well as small details not readily visible on CT scans.

Schott noted that while the team "pursued the project more for validation of MRI as a tool to classify research subjects … it could be used as an earlier diagnostic tool for owners willing to pursue the expense of MRI under general anesthesia."

He cautioned that the procedure is costly, amounting to around $2,000 or so. "I could see the occasional more valuable sport horse at 15-20 years of age being a candidate," he said.

About the Author

Erica Larson, News Editor

Erica Larson, News Editor, holds a degree in Journalism with an external specialty in Equine Science from Michigan State University in East Lansing, Mich. A Massachusetts native, she grew up in the saddle and hs dabbled in a variety of disciplines including foxhunting, saddleseat, and mounted games. Currently, Erica competes in three-day eventing with her OTTB, Dorado. Erica enjoys photography in her spare time.

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