Cushing's Disease

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Equine Cushing’s, also known as Pars Pituitary Intermedia Dysfunction or “PPID”, is a common endocrine disease of older horses.  About 20% of horses over the age of 15 are affected by PPID.  Rarely, PPID can also occur in younger horses.

Horses become affected by PPID when a portion of the pituitary gland develops a benign enlargement.  The pituitary gland sits underneath the brain and plays an important role in regulating hormone levels in the body.  When the pituitary becomes enlarged in horses with PPID, they produce excessive amounts of certain hormones, including Adrenocorticotropic Hormone, commonly known as ACTH.  

The overproduction of hormones can lead to many changes in the horse.  The most common signs we see are long hair coat, slow shedding, increased drinking, increased urination, abnormal sweating, change in attitude, and loss of topline musculature.  Some horses show all of these signs, while other horses may only show one or two.  The stereotypical horse with PPID is always pictured as an older horse with a very long coat that never sheds.  It is still true that horses with PPID can look like that, however, we know now that horses often have advanced PPID before they grow a long, thick coat that doesn’t shed.  The early signs of PPID can be subtle.  

1. Baseline ACTH:   A simple blood test to check a baseline ACTH level.  Horses with moderate to severe PPID will have an elevated baseline ACTH.   Horses with early PPID may have a normal baseline ACTH level.
2. TRH Stimulation Test:  The TRH stimulation test involves giving the horse a dose of Thyrotropin Releasing Hormone (TRH) intravenously and then pulling blood to check their ACTH level 10 minutes later.  Horses with PPID will respond more strongly to the TRH hormone compared to normal horses, so this test allows us to diagnose horses with early PPID. 

PPID can never be cured, however, it can be treated with the medication Pergolide.  Pergolide is available as the FDA-approved medication, Prascend.  Prascend works by blocking the excessive release of hormones from the pituitary gland, which helps to limit clinical signs and improve the quality of life for horses with PPID.