[False positive dexamethasone suppression test in a patient being treated with carbamazepine]

We present a case story of a patient suspected having Cushing's syndrome (CS), with spuriously elevated P-cortisol level diagnosed by overnight and two days dexamethasone suppression test (DST). The patient was being treated with carbamazepine, and after two weeks withdrawal from this drug, both two-day DST and urinary free cortisol showed normal results. There are many pitfalls in the process of diagnosing CS. Several conditions mimic the disease and others cause hypercortisolism. Liver and kidney failure as well as several drugs can influence the test results. It is important to bare this in mind during the diagnostic work-up of suspected CS.