PPID DIAGNOSTIC TECHNIQUE ADVANCES

Year-round diagnosis of pituitary pars intermedia dysfunction (PPID, also known as Cushing’s) just got easier, thanks to the joint efforts of equine researchers in England and mathematicians in Australia.

Caused by an enlarged and overactive pituitary gland, PPID is characterized by overproduction of adrenocorticotrophic hormone (ACTH). This hormonal imbalance can lead to a slew of complications, including a long-haired, slow-to-shed coat, muscle weakness and compromised immunity. PPID also increases susceptibility to laminitis. Although typically found in horses 15 years old or older, PPID can also occur earlier in life.

PPID diagnosis usually requires tests that measure the ACTH levels in a horse’s blood. These levels naturally fluctuate by season, however, which can make interpreting results difficult. “The pituitary gland controls several processes that are seasonally variable---such as reproductive hormones,” explains Andy E. Durham BVSc, MRCVS, of the Liphook Equine Hospital in England. “Exactly why the pars intermedia (a specific areas of the pituitary gland) changes activity through the year is not understood. It might be that this is a process that has

simply remained during evolution and is of no value or benefit to the horse.”

Because ACTH levels are naturally elevated in the autumn, veterinarians used to avoid testing horses for PPID at that time of year. Eventually, more research led to a better understanding of seasonal changes and testing year-round became feasible, though week-toweek fluctuations in hormone levels still complicate the process. Clinicians must weigh the horse’s clinical signs and the test results in making a diagnosis.

To provide clinicians with more accurate baselines, Durham and his team gathered information on ACTH testing in 75,892 horses from across the United Kingdom over a four-year period. In addition to the test results and the exact date the blood was drawn, information from each case included whether the horse had high or low probability of PPID based on clinical signs. An older, laminitic horse with a nonshedding coat, for instance, would fall into “high suspicion” of having PPID group.

All of the data was then sent to a team of mathematicians at Murdoch University in Australia for a series of statistical calculations. “The mathematics part is essentially a rather clever method of examining a lot of ACTH data, some from normal

HORMONAL IMBALANCE: Some signs of pituitary pars intermedia dysfunction—such as a long, slow-to-shed coat—are easy to spot, but a definitive diagnosis of the condition requires a blood test for levels of adrenocorticotropic hormone (ACTH).