Pituitary pars intermedia dysfunction (PPID, or equine Cushing’s disease) has been a challenge for horse owners and veterinarians for years. As researchers learn more information about it, the clinical signs of PPID are becoming more recognizable in horses.
However, there are still several other misconceptions or myths about the disease. Here, Steve Grubbs, DVM, PhD, Dipl. ACVIM, equine technical manager for Boehringer Ingelheim Vetmedica, Inc., dispels some of the most common misconceptions.
Misconception: PPID is only a condition of the geriatric horse.
Yes, PPID is common in senior horses. But, that it only imacts older animals “is probably one of the most common myths about PPID,” Grubbs says. “We have been tracking epidemiological information on horses diagnosed with PPID, and have found that PPID affects horses of all breeds, and all ages, even as young as 5 years old.”
Grubbs adds that it is important to monitor all horses for clinical signs of PPID. “Horse owners should perform frequent overall health checks looking for early signs of PPID,” he says. “If you have concerns, consult your veterinarian. The earlier the diagnosis, the better.”
Misconception: Decreased athletic performance is not a clinical sign of PPID.
One of the earliest signs of PPID, horses showing decreased athletic performance and/or lethargy could have an endocrine issue like PPID. “Catching PPID early on can have a profound impact on how the horse responds to treatment before other signs appear,” Grubbs says.
Misconception: The overnight dexamethasone suppression test is the gold standard for diagnosing PPID.
Once considered the best way to diagnose PPID, the overnight dexamethasone suppression test is no longer recommended by experts to test for PPID. “Instead we recommend using the resting adrenocorticotropin hormone (ACTH) concentration test,” Dr. Grubbs says. “It is a simple blood test that your veterinarian can draw at any time during the day.”
Misconception: Generalized hypertrichosis, or long hair all over the body, is the earliest clinical sign to use for diagnosing PPID.
Generalized hypertrichosis is considered an advanced sign of PPID. “Early signs of PPID include regional hypertrichosis or patchy spots of long hair, delayed hair coat shedding, lethargy, decreased athletic performance, and laminitis,” says Grubbs.
Misconception: Signs of lameness, like tendon laxity and suspensory desmitis, are not associated with PPID.
While laminitis a well-known sign of PPID, until recently other signs of lameness have not been considered to be indicators of the disease. However, new research is indicating that other causes of lameness, particularly certain tendon issues and suspensory desmitis, could also be associated with horses with PPID.
Misconception: For PPID diagnosis, resting ACTH concentrations should not be used during the autumn.
The resting ACTH concentration test can be used at any time of the year, as long as veterinarians utilize seasonally-adjusted reference ranges. “The resting ACTH test is a simple blood test that your veterinarian can draw at any time,” Grubbs says. “The benefits to using this test include not only for diagnosis but also to monitor ACTH levels to know if treatment is working to decrease the levels.”
Misconception: Horses can have only one endocrine disease—either PPID or equine metabolic syndrome (EMS)—but not both at the same time.
The Cornell University diagnostic laboratory amassed more than 3,000 samples to test for PPID from Boehringer Ingelheim Vetmedica’s ID PPID study. “Of those horses diagnosed with PPID, we found that 47% also had increased plasma insulin, which is an indication of EMS,” Grubbs says.