Cushing's Disease in Horses
(Pituitary Pars Intermedia Dysfunction)

Neonatal Isoerythrolysis (NI) is a life-threatening hemolytic disease of foals caused by ingestion of colostrum containing antibodies against the foal’s red blood cell antigens. This immune-mediated condition typically affects foals born to mares previously sensitized to foreign erythrocyte antigens, most commonly Aa or Qa.

Equine Cushing's Disease, also known as Equine Pituitary Pars Intermedia Dysfunction (PPID), is a chronic, progressive condition primarily affecting older horses, typically over 15 years of age. This disease is rooted in the intermediate pituitary gland, where abnormal growth leads to excessive hormone production, particularly cortisol. Common clinical signs include hirsutism (long, curly hair coat that doesn't shed properly), polyuria and polydipsia (excessive drinking and urination), laminitis, lethargy, increased sweating, and muscle mass loss. Horses with PPID may also exhibit insulin resistance, which contributes to various symptoms like abnormal fat accumulation and laminitis.

Diagnosis is often based on clinical signs like hirsutism in aged horses, with the dexamethasone suppression test and measurement of resting plasma ACTH concentration being commonly used tests. However, these tests have limitations, including seasonal variations in their accuracy. Other tests, such as the TRH test and the domperidone test, are used in research settings.

Treatment focuses on managing symptoms and enhancing quality of life rather than achieving complete disease remission. Pergolide is the preferred medication, with dosage adjustments based on therapeutic response. Supportive care includes regular deworming, dental care, farrier work, and dietary management, especially in insulin-resistant horses.

References:

1. American Association of Equine Practitioners. Equine Endocrinology.