In this article our laboratory expert, Stacey A Newton, BVSc, FRCPath, CertEM (Int Med), PhD, MRCVS, explores the diagnosis of equine metabolic syndrome (EMS), also known as atypical Cushing’s disease or peripheral Cushing’s disease. EMS is a condition characterised by significant peripheral insulin resistance, obesity, laminitis, and insulin dysregulation (ID). The diagnosis of EMS requires a combination of history, clinical signs, and diagnostic tests, taking into account the effect of season and the individual’s current health status.

The article highlights the importance of evaluating obesity, ID, and dyslipidaemia as key factors in diagnosing EMS. It also discusses the use of various diagnostic tests, including:

• Basal cortisol levels: Elevated cortisol levels may indicate EMS.
• Insulin levels: Elevated insulin levels may indicate ID.
• Overnight dexamethasone suppression test: Negative results can help differentiate EMS from equine pituitary pars intermedia dysfunction (PPID).
• Insulin resistance tests: In-feed oral sugar test (OST) or oral glucose test (OGT) can be used to assess insulin resistance.
• Combined insulin-glucose tolerance test (CGIT): This test is no longer recommended for routine clinical use due to its complexity and expense.

The article also notes that the sensitivity and specificity of these tests can be affected by various factors, including season, and that there is no gold standard for diagnosing EMS.

The article concludes that a diagnosis of EMS requires a combination of detailed history, clinical signs, and diagnostic tests, taking into account the effect of season and the individual’s current health status. It emphasises the importance of considering the diagnosis of EMS in horses with obesity, laminitis, and insulin dysregulation.