Equine Metabolic Syndrome versus Pituitary Pars Intermedia dysfunction (PPID) a.k.a. “Cushing’s Disease”
Overlap of clinical signs exists between EMS and Cushing’s disease (pituitary pars intermedia dysfunction [PPID]). Regional adiposity, insulin resistance (IR), and laminitis occur in both disorders, but EMS can be distinguished from Cushing’s by the following characteristics: age on onset (EMS tends to occur in younger horses [<15 years] where as Cushing’s tends to occur in older horses) and clinical signs such as delayed shedding of the winter coat, increased drinking and urination, and skeletal muscle atrophy are suggestive of Cushing’s.
Given the similarities in between EMS and Cushing’s, horses with regional adiposity and laminitis should be tested for Cushing’s in addition to EMS, especially horses over 15 years of age with the clinical signs described above. Insulin resistance can be attributed to EMS if there is no evidence of Cushing’s. In horses and ponies with EMS, ACTH (adrenocorticotropin hormone) are within reference range and cortisol is suppressed by dexamethasone administration (dexamethasone suppression test). These tests should be performed outside the late summer/fall period(Aug-Nov), which are times of the year when false positives occur in healthy horses and ponies. We recommend working with your veterinarian to differentiate between PPID (Cushing’s) and EMS.
Occasionally both disorders can occur together. Some horses with EMS will later develop Cushing’s. Horses and ponies with EMS should be monitored for signs of Cushing’s development such as delayed shedding of winter coat or increased drinking and urination.
*This project was supported by Agriculture and Food Research Initiative competitive grant no. 2009-55205-05254 from the USDA National Institute of Food and Agriculture Animal Genome Program.