Equine Cushings (Pars Pitutary Intermedia Dysfunction – PPID)

This is one of the most common endocrine conditions affecting equine geriatric populations especially those over 15 years of age.

Also known as hyperadrenocorticism, it’s common among ponies and Morgans as compared to horses probably due to their long life span (1).

Equine Cushings is linked to disturbances affecting the pituitary gland. The pituitary gland lies at the base of the brain. It is responsible for the secretion of various hormones in the body which stimulate other glands to produce hormones that drive body physiological processes. A case of PPID occurs when a tumour known as pituitary adenoma grows on the middle lobe (pars intermedia) of the pituitary gland. This causes an over secretion of a hormone known as adrenocorticotropic hormone (ACTH) which consequently stimulates the adrenal gland to produce an excessive amount of a hormone known as cortisol.

High cortisol levels in the bloodstream lead to various changes in the body. These include:
• Hirsutism. This usually is a distinctive sign of PPID. It refers to when horses have long curly hair due to lack of shedding. The skin also appears dry, flaky and thin.
• Polydipsia and polyuria. This is the excessive drinking of water and urination
• Weight loss
• Increased appetite
• Excessive sweating
• Blindness. This is results from pressure exerted on the optical nerve as a result of the enlargement of the pituitary gland.
• Laminitis- Inflammation of the soft tissues of the hoof.
• Suppressed immunity indicated by the recurrence of infections e.g. sinusitis, abscesses
• Bulging eyes are also a common occurrence due to excessive deposition of fat around the eye socket.
• Infertility

Insulin resistance is also observed in affected equines. Insulin is a hormone produced by the pancreas which enables tissue cells to take up glucose from the bloodstream for energy production with the excess glucose stored as fat for future body needs. Insulin resistance occurs when body tissues are unable to respond to insulin resulting in some of the above signs e.g. Lethargy, increased appetite, laminitis, weight loss, unequal distribution of fat etc.

Distinctive increased coat length of PPID / Cushing’s disease (Photo courtesy of Dr Nicola Menzies Gow) (2)

Treatment
Treatment usually does not resolve the condition but is geared towards improving the quality of life of the horse. A veterinarian should be contacted if any of the above signs are observed.

References
1. Dana Zimmel, DVM, DACVIM D. Management of Equine Cushing’s Disease and Equine Metabolic Syndrome. Florida; :0–3.
2. Royal Veterinary College U of L. Equine Cushing’s disease [Internet]. [cited 2018 Jul 25]. Available from: https://www.rvc.ac.uk/equine-vet/information-and-advice/fact-files/cushings-disease#panel-clinical-signs