Description Pituitary pars intermedia dysfunction (PPID), commonly known as Equine Cushing’s Disease, is a progressive disorder disrupting the horse’s endocrine (hormonal) system, typically affecting middle-aged to older horses. In horses Cushing’s disease is almost exclusively caused by enlargement - hypertrophy (increase in cell size) and hyperplasia (increase in cell number) - of the pars intermedia (intermediate lobe) of the pituitary gland, thought to be due to a decreas