Pituitary Pars Intermedia Dysfunction (PPID/Equine Cushing’s Disease)

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What is PPID?

Pituitary Pars Intermedia Dysfunction (PPID), also known as Equine Cushing’s Disease, is a common disease of older horses and ponies. The disease becomes increasingly common as horses get older and affects over 25% of horses and ponies over 15 years old. The disease affects the pituitary gland which is located at the base of the brain. In PPID, part of the pituitary gland becomes over-active and produces greater amounts of some hormones. These hormones can affect other parts of the horse and cause the symptoms of PPID.

What are the signs of PPID?

The effects of PPID can vary a lot between cases. Some of the clinical signs include:

  • Coat changes (increased coat length and/or failure to shed coat normally)
  • Weight loss
  • Abnormal fat deposits
  • Muscle wastage
  • Increased drinking and urination
  • Lethargy
  • Impaired immune function and thus increased susceptibility to infections
  • Laminitis

How is PPID diagnosed?

There is no perfect test for diagnosis. Vets make decisions based on:

  • History – the owner’s description of their horse and their symptoms.
  • Clinical examination – the vet’s findings when examining the horse.
  • Blood tests for hormone levels (basal plasma Adrenocorticotropic Hormone (ACTH) concentration or Thyrotropin-Releasing Hormone (TRH) stimulation test). The most useful test and the interpretation of the results changes through the seasons.
    • Sometimes these blood tests give a clear positive or negative result but results may also be in a ‘grey area’ in between positive and negative and vets can use other information such as the horse’s symptoms to make treatment decisions.

How is the disease treated and managed?

Changes to horse management (such as coat clipping and diet changes) and medicines can be helpful in PPID. Since clinical signs and their severity differ between animals, strategies should be tailored to individual horses’ needs.

  • Medicines – Pergolide (most known under the trade name Prascend) is the only licensed drug for the management and treatment of PPID. Pergolide is generally an effective medicine and significant side-effects are uncommon. Side effects can include reduced appetite, depression, diarrhoea, and colic.
  • Management changes – These may include feed modifications, managing turnout on grass and preventative health care.
  • There is no cure for PPID and affected animals will require lifelong treatment and/or suitable husbandry management.