Pituitary pars intermedia dysfunction (PPID) is an endocrine disease that is thought to affect between 15-30% of aged horses. Commonly referred to as 'Cushings disease', PPID is caused by degeneration of nerves that release dopamine in the pars pituitary intermedia, a portion of the pituitary gland near the brain. The average age of diagnosis is 20 years. The most obvious clinical sign in more advanced cases is hypertrichosis or hirsutism (hair growth, abnormally long curly hair, and/or a failure to shed out normally in the summer). Other clinical signs can include increased drinking and urination, chronic infections, muscle wasting, weight loss, regional fat deposits, and an increased propensity to develop laminitis (founder).
Testing for PPID involves a simple blood test that measures the levels of ACTH (adrenocorticotropic hormone) in the blood. The blood must be kept refrigerated after collection and centrifuged and separated soon after, so it is best to do the test in the morning if possible. Results take 1-2 weeks to return.
The treatment of choice for PPID is a medication called pergolide, which is marketed as Prascend. It is an oral medication in pill form that is given once a day for the remainder of the horse's life. Adverse reactions to this medication are quite uncommon, and it works very well to control clinical signs in the majority of horses. Ideally, the ACTH levels in the blood would be rechecked once or twice yearly in order to determine if the disease is being well controlled and if the medication dose should be adjusted.
Because this disease occurs in older horses, it is often missed as the owner assumes that their horse isn't looking and feeling as well merely because they are getting older. In the initial stages, the typical abnormal hair growth may not yet be present, and you may just notice that the horse has less energy and looks thin and poorly muscled. Many owners report that it is almost like getting their old horse back when they start treatment. The following is a report of one such case in a horse used for competitive polo, written by her owner Connie:
"Flor has always been a horse who gives everything she has. During the playing season of the summer of 2013, I noticed that she wasn’t playing as hard as she had in previous years. Sometimes she would just give up the chase, something she had never done in the past. At the age of 19, I thought she was getting old and just didn’t want to play anymore. Then in the spring of 2014 I noticed that she was not shedding out her winter coat, still hanging on to it well into June. And again, she just didn’t seem to have the energy to play hard, a behaviour that was very atypical for Flor. I decided to have her tested and she was diagnosed with PPID. I started her meds as soon as I received the diagnosis. Within 4 days, she started shedding out significantly. I played her in a tournament only 7 days after having started her on the meds, and in that tournament she played with an energy level I hadn’t seen in her in nearly two years. Additionally, her entire demeanour changed; she had seemed depressed, but now I could see a brightness in her eyes, signs of just feeling better overall. To me, it felt as though I had my horse back! She continued to play for the rest of the season with the enthusiasm and drive that I had come to expect from her. I was astounded by the change in her, and also by how quickly I noticed the change once I had started the meds. It is rewarding to know that with such a simple treatment, she now feels like her former self."