Topiramate as a Cause of False Positive in the Overnight 1-mg Dexamethasone Suppression Test

To describe that topiramate may cause a false positive in an overnight 1-mg dexamethasone suppression test (DST) for hypercortisolism screening.

We present a case in which topiramate induced dexamethasone metabolism, leading to a false positive on the DST.

A 44-year-old female with an incidentally found adenoma in the right adrenal gland underwent a DST for hypercortisolism screening. The patient was taking topiramate prescribed by a psychiatrist for an affective disorder, and insufficient cortisol suppression (11.9 mcg/dL) was observed. Her free cortisol in 24-hour urine was normal, and insufficient suppression was established in a second determination (9.3 mcg/dL). Finally, her psychiatrist switched her treatment from topiramate to bupropion, and the measurements were repeated. When she was not taking topiramate, correct suppression with 1 mg of dexamethasone was obtained (1.7 mcg/dL), and her free cortisol in 24-hour urine was again normal, thereby excluding the presence of hypercortisolism. On reviewing the literature, topiramate was not found to have been previously described as a cause of a false positive on DST, but it was proposed as a cause of hypoadrenalism in a patient taking oral corticosteroid replacement due to its capacity to induce dexamethasone metabolism.

Topiramate treatment may well be a cause of false positives in DSTs, and its presence should be taken into consideration when screening for hypercortisolism.