Equine Cushings-like Syndrome (PPID)

By Nick Page, BVSc

Before getting into the detail of this disease, let’s first clarify a little terminology: Equine Cushings disease, as it has traditionally been called, is an incorrect use of the term. The disease known as Cushings involves a tumour growth which secretes hormones in one portion of the pituitary gland known as the pars distalis. This is not the case in equine Cushings-like syndrome, where the condition does not involve tumour growth at all. Instead, this disease is caused simply by the over-secretion of hormones and generalised enlargement (hypertrophy) of a part of the pituitary gland known as the pars intermedia. Therefore, a better term would be Cushings-like syndrome or more accurately Pituitary Pars Intermedia Dysfunction (PPID).
To understand this further the normal concept of corticosteroid control in the body needs to be understood. Cortisol is the stress hormone secreted by the cortex of the adrenal glands. This is released after stimulation by a separate hormone known as ACTH which is produced in the pituitary gland. Normally excessive circulating cortisol causes reduction or cessation of secretion of ACTH via Dopamine levels rising in the pituitary gland.
PPID occurs through a failure of this process within the pituitary gland, which results in excessive secretion of ACTH and several other hormones by the pars intermedia of the pituitary gland. The disease process is thought to be very similar to that causing Parkinson’s Disease in humans.
PPID appears much more commonly in older middle-aged to aging equids. Certain species and breeds appear more at risk of developing the disease (Morgan horses, ponies and possibly donkeys).
The resulting clinical signs resulting are wide-spread and include excessive hair growth, excessive sweating, redistribution of fat, excessive thirst and hunger, immunosuppression and risks to parasitism and infectious diseases and very importantly a significant propensity to develop laminitis.


The laminitis symptoms are thought to result from the influence of excessive cortisol secretion on blocking the effects of insulin on target cells, which in turn can directly result in constriction of small arterioles supplying oxygenated blood to the foot. Also, this can result in a type-2 diabetes situation similar to humans resulting in high levels of circulating glucose, which causes similar vascular effects as described above.
The result is that the cells of the laminae of the hoof get inadequate oxygen supply and die. This results in laminitis, the details of this specifically can be covered in a future article.
PPID should not be confused with Equine Metabolic Syndrome (EMS), which is a separate stand-alone disease. EMS also commonly results in laminitis, but its diagnosis and treatments are different from that of PPID. 

Dr Nick Page has been a practicing veterinarian for over 20 years now. He has a passion for surgical diseases and treatment and throughout his career has amassed specific skills in more advanced surgical treatments and diagnostics associated with surgical diseases. Nick has a specific interest in equine medicine He holds administrative and clinical roles with Equestrian Sport New Zealand with a portfolio in the Endurance discipline .
Nick practices at Rolleston Veterinary Services in Rolleston, NZ .