1. What is PPID?

Previously known as Cushing’s disease, pituitary pars intermedia dysfunction (PPID) occurs when the pituitary gland becomes enlarged and overactive, producing excessive amounts of adrenocorticotropic hormone (ACTH). These elevated ACTH levels, in turn, lead to increased cortisol production. Although the exact of PPID cause remains unclear, the condition is especially common in senior horses. Researchers on one study found that 85% of veterinarians are caring for at least one horse with the condition.

2. How Does PPID Affect Horses?

Elevated hormone levels lead to a wide range of clinical signs in horses with PPID, such as a long hair coat that is slow to shed, muscle-wasting, lowered immune function, and susceptibility to infection. Many affected horses also develop slow‑onset chronic laminitis, which might go unnoticed until hoof structures have been significant and irreversibly damaged.

3. How is PPID diagnosed?

In addition to observing clinical signs, veterinarians utilize two laboratory tests to diagnose PPID. The first is a blood test to measure resting ACTH levels. The second is the thyrotropin-releasing hormone stimulation test (TRH stimulation test), which involves taking a blood sample, giving an injection of TRH, and then collecting a blood sample again 10 minutes later. All horses show some increase in ACTH after TRH administration, but horses with PPID exhibit a significantly greater rise. Because of natural seasonal and geographic fluctuations in ACTH, veterinarians use published reference ranges to interpret laboratory results.

4. Is there an effective treatment for PPID?

Yes, PPID can be treated with pergolide, a medication sold under the brand name (Prascend) and as a generic product (Zygolide). Pergolide acts on dopamine receptors in the brain, reducing ACTH production. It is given daily and is widely considered the most effective treatment for controlling PPID.

5. What does the latest research tell us about PPID?

Pituitary pars intermedia dysfunction is the subject of continued research, and recent studies offer encouraging results.

• Researchers from Michigan State University followed 30 horses from the original 2011 Food and Drug Administration efficacy study for an additional 15 years evaluating the long‑term safety and effectiveness of pergolide. Five years into the study, all owners reported consistent improvement in their horses’ clinical signs, and nearly 60% of the horses had normal endocrine test results. Ten years into the study, 96% of horse owners agreed pergolide had improved their horses’ quality of life. What’s more, the researchers found no indication that horses developed resistance to pergolide over time.

• Researchers from Purdue University found that if managed with medication, PPID is not likely to shorten a horse’s lifespan. They examined the records of 132 horses diagnosed with the condition, along with the records of 274 healthy horses to serve as controls. Almost all the PPID horses—94.7%—were on a treatment regimen that included medication. The scientists found that although horses with PPID were indeed more likely to develop dental issues, laminitis, and impaired wound healing, they did not die any earlier than horses without the condition.