PPID (Equine Pituitary Pars Intermedia Dysfunction) is a disease of the horse’s brain. It is caused by damage to the nerves that control secretion of hormones by the pituitary gland. Pituitary hormones include regulation for Cortisone, Thyroid Hormone, Hair growth, Urination, Lactation, and Reproduction. Loss of control usually causes elevation of the various hormones, although sometimes it just mean loss of the normal up and down cycles that occur daily.
The signs of PPID are related to which hormones have gone out of control. The most commonly observed ones are ACTH, which regulates body cortisone levels, MTH, which regulates hair growth, and ADH, which regulates production of urine. As you might expect, the horse shows these problems by urinating too much, growing too much hair, or getting a large abdomen or foundering. Horses that show the typical long dreadlock type hair are obvious. The urination and reproductive issues must be tested for , indirectly, by looking at kidney, urine, and reproductive hormone levels. Cortisol is best evaluated indirectly by measuring ACTH levels, although there are older tests such as the dex suppression test that can also be used. Detecting cortisol elevations is vital because of the increase in insulin resistance it causes, as well as the direct suppression of the immune system and liver damage.
Once diagnosed, the treatment of PPID is medical, and the goal is to return hormone levels to normal. Fortunately, we now have available a prescription medication to treat the disease called Prascend. Prior to the availability of Prascend, we were forced to use compounded pergolide, which was shown in multiple studies to be very unreliable and unstable. Prascend causes ACTH to go down to normal levels when dosed correctly in over 90% of the horses. It is important to monitor the ACTH level at least twice yearly to be sure the ACTH is staying in the normal range. There is a fall rise in the normal level of ACTH in August through December, and it is exaggerated in PPID patients. This elevation causes an increase in insulin resistance, and is responsible for the fall laminitis episodes that occur each year.