Equine pituitary pars intermedia dysfunction (PPID) was first identified in the 1930’s as equine Cushing’s disease. At that time, it was considered a rare complication of old age in horses. It was renamed PPID in the late 1990’s when researchers recognized the variations in the disorder between horses vs. people and dogs.
PPID is a malfunction of the pituitary gland, resulting from a tumor or an enlargement of the gland, which puts pressure on the hypothalamus. This, in turn, causes reduced production of dopamine. Without naturally regulated levels of dopamine, the pituitary cells secrete uncontrolled amounts of hormones, including high levels of the steroid cortisol. Increased cortisol levels result in a depressed immune system that causes varying degrees of symptoms.
The most common symptom of PPID is hirsutism (abnormal hair). A shaggy, long, thick, frequently curly, hair coat is often preceded by years of subtle coat variations. Hyperhidrosis (sweating) leads to discomfort and health complications, especially in the winter months in cold regions. Other common clinical signs and symptoms include more susceptibility to internal parasitic invasions, sinusitis, sole abscesses, muscle wasting, extreme thirst, frequent urination, periodontal disease, skin infections, swayback, potbelly, laminitis and pneumonia.
The average age at which horses contract PPID is 20 years, with 85% older than 15 years at the time of diagnosis. Although ponies over the age of 15 years have a very high incidence of the disease, a gender or breed predisposition in horses is not apparent. The veterinary community is seeing a large increase in reported PPID cases, mainly due to horses' unprecedented longevity, which is now possible because of advanced medical care, parasite control and nutrition.
The pharmaceutical treatment options available for PPID actually target the source of the problem. The most significant treatment is the use of pergolide, a dopamine therapy. This drug is also used in human patients with Parkinson’s disease. In humans, the patient eventually becomes resistant to pergolide but in horses, there are no signs of resistance developing. It is suspected that the low dosage required for horses is minimizing this effect. The serotonin blocker cyproheptadine is another option, though there is inconsistent evidence of a therapeutic benefit of this drug.
Natural options include magnesium supplementation, acupuncture, homeopathy and herbal medicines. Though some have found success in natural regulations, it requires a very intense regimen to find a balance that will make your horse comfortable. In the meantime, he is subject to a battery of conditions of which infections and laminitis are the primary concern.
Management measures include diet, antioxidant supplements, parasite control, dental care, farriery and body clipping. As with insulin resistant horses, a low-carbohydrate/high fat diet is recommended. Limit your horse’s access to lush pasture grasses. Grass hays are a safer option than legumes (clover, alfalfa) because they contain fewer carbohydrates.
Extensive testing for PPID involves a complete blood count (CBC), clinical chemistry panel and urinalysis; followed by a two day testing for PPID specifically. PPID horses have a better prognosis than ever before. With proper treatment and management, they can enjoy long and productive lives.