We all have seen the pictures of the classic “Cushing’s” horse: long, curly hair, weak topline, pot-bellied and aged. This is the advanced stages of a disease that can start at a younger age, where subtle changes can be easily overlooked. The Arabian mare above was diagnosed at 13 with early stage PPID after her owners observed changes in her topline and haircoat.
What is PPID?
Pituitary Pars Intermedia Dysfunction (PPID), formerly known as Equine Cushing's Disease, is the most common endocrine disease in horses. It is cause by the formation of small tumors within a specific portion (pars intermedia) of the pituitary gland, an organ at the base of the brain. These tumors are 'functional,' meaning they are able to secrete hormones as the pituitary gland does. Their secretion of hormones leads to a surplus of these natural hormones, the most problematic being ACTH, which stimulates the adrenal glands to secrete cortisol, the body's 'stress hormone.' This subsequent increase in these specific hormones in the body causes the symptoms (listed below) that we associate with clinical PPID.
Clinical signs of PPID
Lethargy and/or decreased athletic performance
Delayed shedding or failure to fully shed
A long, sometimes curly, hair coat
Loss of muscling (especially along topline)
Increased water intake and increased urination
Abnormal mammary gland development
How do you test for PPID?
The most common test for PPID is a simple blood test for plasma ACTH levels. There is seasonal variability in ACTH levels, so the best time to perform this test is September and October. At other times of the year, the TRH–stimulation test is used. This involves taking a blood sample, giving an injection of TRH (thyrotropin-releasing hormone) and then taking a second blood sample 10 minutes later. The ACTH levels of the samples taken pre- and post-TRH are evaluated and compared to determine if the horse has PPID. This test is most accurate if performed between December and June. For earlier or more subtle cases, it may be recommended to perform the more sensitive TRH-stimulation in the spring versus the single ACTH in the fall.
How do you treat PPID?
PPID is not curable but the clinical signs
can be managed with a daily medication called Prascend (pergolide mesylate). The medication decreases hormone production in the pituitary gland, thus alleviating many of the clinical signs listed above.
In summary, PPID is an endocrine disease most routinely diagnosed in older horses, that can be managed but not cured. The most common signs of lethargy and a long hair coat are only the tip of the iceberg when it comes to the clinical manifestations of this disease. Early diagnosis and management can help lower the risk of the more dangerous complications of PPID that include laminitis and an increased risk of infection.
The mare was started on Prascend and, as a result, her topline and haircoat have improved and her energy level has increased. While her disease will continue to have to be monitored throughout her life, the early diagnosis and treatment have returned her to her pre-symptom, feisty self.
The Equine Endocrinology Group, made up of clinicians and researchers, work together to study, review and revise diagnostic and treatment recommendations for endocrine disorders in horses. Check out their website for more information about the work of this important group.
For questions about PPID, or to schedule testing for your horse, please don’t hesitate to contact us by phone at (253) 535-6999 or via email at firstname.lastname@example.org.
Originally published Oct 2016. Updated April 2021.