Equine Cushing's disease was first described in 1932. Until recently it was considered to be caused by a benign tumor leading to pressure on certain parts of the brain and thus causing changes in the horse's hormone levels.
Recent research has shown that Equine Cushing's is nothing like Cushing's disease (Hyperadrenocorticism) in humans and dogs, for example. Therefore the name equine Cushing's disease should be avoided and has been replaced with PPID, which stands for Pituitary Pars Intermedia Dysfunction. It is the name of the part in the horses brain that is actually affected by the disease. We know now that it is NOT caused by a tumor, but it is now actually considered a " neurodegenerative" disease. The formation and accumulation of misfolded "neuroproteins" seems to cause the dysfunction in the pars intermedia of the equine pituitary gland. Although there is no resemblance to true Cushings disease, we know now that this neurodegenerative disease has in some aspects more similarity with human Parkinson's disease.
While me measure ACTH in blood to test for PPID in horses, the cortisol levels in the blood are hardly ever elevated in affected horses, because the ACTH that is produced in abundance by the pituitary gland is not partially not hormonally active and cannot trigger increased cortisol production of the adrenal glands.
Looking at the connection between laminitis and PPID and it seems that the increase of blood Insulin levels is the trigger or better the biggest risk factor for laminitis. PPID increases the risk for these horses with Hyperinsulinemia
For more formation about Equine Metabolic Syndrome check out our first blogpost and the link to UoM.
You can find more information and a list of possible clinical signs of PPID here
For more in depth information visit: the Equine Endocrinology Group website
ref: Pathophysiology and clinical features of pituitary pars intermedia dysfunction
D.Mc Farlane EVE 11/14
