What Is Pituitary Pars Intermedia Dysfunction (PPID)?
Cushing’s disease in horses is a slowly progressive disease of the pituitary gland in the brain in middle aged to older horses. Ongoing degeneration of neurons in the hypothalamus that normally inhibit the pituitary with dopamine lead to an overgrowth of the gland and overproduction of the hormones it produces, including ACTH. Excess hormone production leads to the clinical signs we see.
Clinical Signs of PPID
Clinical signs can vary greatly depending on stage of disease and the particular cells of the pituitary that are affected. Here are some common signs we see:
- Change in Attitude
- Areas of excess hair growth
- Delayed hair coat shedding
- Loss of topline muscle
- Weight loss due to muscle atrophy
- Abnormal sweating ( or ¯)
- Regional fat deposits
Advanced Disease may also include:
- Dull Attitude or altered mentation
- Exercise intolerance
- Generalized excess hair growth
- Loss of seasonal hair coat shedding
- Topline muscle atrophy
- Rounded Abdomen
- Excessive Drinking/Urinating
- Recurrent infections/Delayed healing
- Dry Eye/Recurrent Eye Ulcers
- Mammary gland secretions
- Tendon/ligament laxity
- Laminitis with recurrent hoof abscesses
- Baseline ACTH Plasma Levels – Current circulating levels of ACTH levels in the blood
- TRH Stim Test à ACTH Plasma Levels – Horses in early stages of the disease may not be secreting consistently high ACTH levels at the time of the blood draw. This test, performed in 10 min on the farm, will stimulate pituitary gland to release ACTH. While there is an expected increase from baseline in all horses, those with PPID have a higher response. This test is ideally performed at least 12 hours after the last grain meal.
- Since approximately 30% of horses with PPID also have insulin dysregulation, it is ideal to test baseline insulin values at the same time.
Time of year: ACTH levels naturally rise in all horses during the late summer and fall months. We can still test during this time of year using seasonally adjusted reference ranges. Horses with PPID tend to have an exaggerated response to seasonal changes.
If your horse’s baseline ACTH value falls in the grey zone between negative and positive, we can perform a TRH stim test, retest in 3 to 6 months, or start treatment if clinical signs, especially laminitis, are present.
While there is no cure for PPID, medication can help slow progression and manage clinical signs.
>>Prascend (pergolide) acts like dopamine to inhibit growth and activity of pituitary gland.
The most common side effect of this medication is loss of appetite. For this reason, we suggest starting at a lower dose before increasing to the intended initial dose.
After 1 month of, you may notice improvement in clinical signs such as improved attitude or performance, increased activity levels, improvement in excess drinking/urination, and improving sweating regulation.
After 2 months, ACTH levels should be re-tested. If the ACTH levels are still increased, we will adjust the dose accordingly.
Once ACTH levels are stable and we are seeing a positive clinical response, ACTH levels should be retested every 6 to 12 months. As your horse ages, the dose of prascend may need to be increased to accommodate disease progression.
In addition to medicine, horse’s with PPID should receive regular consistent wellness care:
- Annual dental exams – Older horses often require frequent dental care and horses with PPID are more prone to bacterial infections from dental disease. If you notice bad breath, nasal discharge, or dropping feed/quidding, please schedule a dental exam sooner.
- Parasite control – Annual fecal egg counts should be performed to assess parasite shedding and types of worms present. Even if this count is low, horses should be dewormed annually with an ivermectin or moxidectin combined with praziquantel for tapeworms (ideally given in fall/winter after the first frost).
- Adequate Nutrition and Feeding Plan – Please discuss your horse’s diet with your veterinarian. Recommendations will vary based on presence of insulin dysregulation, body condition score, and dental disease.
- Always provide fresh, clean water even if your horse drinks excessively.
Monitoring – Please call us with any new concerns
Watch for any signs of infection or wounds including swollen/squinting eyes, skin lesions, fever, lethargy, diarrhea, or thick discharge from any area.
Watch for signs of laminitis including divergent hoof rings, tender feet on a hard surface/gravel, lameness at the walk (especially in a tight circle/turn), not wanting to walk forward, weight shifting between legs, rocking back on hind feet, parking out, or laying down more frequently.
Watch for progression of other clinical signs associated with PPID
The prognosis of horses with PPID can vary greatly based on severity of disease and response to medication. Many horses will live for years with this disease. It is important to keep a regular relationship with your veterinarian to monitor your horse’s quality of life.