Equine Cushing’s Disease or Equine Pituitary Pars Intermedia Dysfunction (PPID) Keeping up with Evolution

In 1932, Pallaske reported a condition in geriatric horses that resulted in a long, curly hair coat and an enlarged pituitary gland [1]. This disease, known as Equine Cushing’s Disease, or re-named as equine pituitary pars intermedia dysfunction (PPID) is now commonly recognized in equine practice, partly because of the increasing geriatric equine population. PPID is a primary problem of the pituitary gland, located beneath the brain. This gland is like a dispatch center, where hormones and other chemical mediators called proopiomelanocortin peptides (POMC) are produced and then released into the body to control body functions. PPID is a naturally occurring, progressive condition characterized by hypertrophy and hyperplasia of the pars intermedia of the pituitary gland resulting in an increased expression of POMC peptides [2]. Horses with PPID have a breakdown of the control of the pituitary gland – it literally doesn’t shut down and continues to produce POMC. Affected horses have an increased circulating concentration of POMC-derived peptides, ultimately leading to the development of clinical signs through a sequence of events that was poorly understood until recently.