Pituitary Pars Intermedia Dysfunction (PPID) / Equine Cushing’s
PPID or Equine Cushing’s disease is a common disease of older horses ( >15 years of age). It is thought that approximately 1 in every 7 horses over 15 years of age has PPID (14% - 30 %). Less commonly, it can also be present on younger horses.
What is PPID?
PPID consists of a dysregulation of the normal functioning of the hypothalamic-pituitary-adrenal axis. This dysregulation in the secretion og hormones has consequences to your horse’s health.
There are still aspects of PPID condition that are not fully understood, including the exact cause of this dysfunction. It is thought, however, that oxidative damage results in a loss of inhibitory dopaminergic neurons, causing the horse’s pituitary gland to overwork.
Ongoing research is focused on the relationship between PPID, chronic laminitis and Insulin Resistance.
Does my horse suffer from PPID? What does PPID lead to?
There are several different diagnostic tests that can be performed, but there are several clinical signs that horse owners should keep an eye for:
- Unusual hair growth/shedding / Hirsutism:
- Severity and presentation varies: long hair patches in certain areas of body, incomplete shedding of winter coat or delay in doing so, unusual whisker growth, change in coat color or fully overgrown hair.
- Also very frequent in PPID horses. The relationship between PPID and Insulin Resistance and the effect of glucocorticoids is thought to play a part in the development of laminitis in these horses. Up to 70% laminitic horses have PPID.
- Fat redistribution / weight loss:
- ”Potbelly appearance”, fat around the eyes, top of the neck, tail head.
- Lethargy / Poor performance:
- Affected horses often look dull or do not perform as expected (often goes unnoticed). This is one of the earliest signs.
- Polydipsia / Polyuria:
- Increased thirst (and intake of water) and increase urination.
- Excessive sweating.
- Delayed wound healing and increased susceptibility to infections.
- Neurological signs.
- Increase in docility is often reported by owners of PPID horses.
A thorough clinical exam conducted by a qualified veterinarian is necessary to evaluate different aspects of your horse’s health and to decide if it is appropriate to proceed with blood testing, and if so, which tests. There are several tests available to help obtain a better understanding of a horse’s health and whether or not it suffers from PPID. Some of the most common are listed below:
- Plasma ACTH (AdrenoCorticoTropin Hormone) concentration:
- This test involves collection of a blood sample from your horse at a specific time of day and interpretation o fresults after proper processing of the sample. There is an increase in ACTH secretion both in normal and PPID horses during the autumn.
- Dexamethason Supression Test:
- This test involves the collection of several blood samples at specific times and the administration of a dose of dexamethasone. Interpretation of blood values of cortisol provides the veterinarian with information on pituitary function. Also affected by season among other things.
- TRH stimulation Test:
- This test involves collection of several blood samples at specific times and administration of TRH (Thyrotropin Releasing Hormone)
Unfortunately, there is no cure for PPID, BUT clinical signs can be improved and horses can have many years of good quality life with treatment.
- Pergolide mesylate (Prascend®)
- This drug is a dopamine receptor agonist. It stimulates dopamine receptors and helps control clinical signs of PPID.
- In one study, 72% of horses with hirsutism show significant improvement after 56 days.
- Laminitis symptoms improve in 80% of horses who are treated for PPID.
- Most horses respond in between 6-12 weeks.
- There is evidence that treated horses live longer than untreated horses.
- This is a daily, lifelong drug.
- Other drugs (cyproheptadine, bromocryptine, cabergoline, trilostane, metyparone, etc.)
- Monitoring and management of associated secondary problems ( laminitis, weight loss, etc.)
After treatment is initiated, careful monitoring and routine blood tests should be performed to achieve minimal effective dosage and maintenance of a healthy horse.