From the Research
Topiramate may cause a false positive in the overnight 1-mg dexamethasone suppression test (DST) for hypercortisolism screening, but it does not significantly affect serum AM cortisol levels. This is based on a case study published in 2014 1, which reported that topiramate induced dexamethasone metabolism, leading to a false positive on the DST. However, the study did not find any significant effect on serum AM cortisol levels.
Key Points to Consider
- Topiramate's effect on the dexamethasone suppression test is due to its ability to induce dexamethasone metabolism, rather than a direct effect on cortisol production 1.
- The overnight 1-mg dexamethasone suppression test is a reliable screen for Cushing's syndrome in obese patients, with a false positive rate of 2.3% 2.
- Other studies have reported that the low-dose dexamethasone suppression test may yield false-negative results in some patients with Cushing's syndrome 3.
- The use of ACTH following overnight dexamethasone suppression as a marker of HPA axis suppression may help to verify autonomous cortisol secretion in patients with adrenal incidentalomas 4.
Clinical Implications
- Patients taking topiramate for epilepsy, migraine prevention, or other off-label uses can generally undergo cortisol testing without needing to discontinue their medication.
- However, clinicians should be aware of the potential for topiramate to cause false positives on the DST and consider the patient's overall clinical picture when interpreting test results.
- If precise cortisol measurement is critical for diagnosis, clinicians should ensure the patient is in a stable condition when testing is performed and consider using alternative tests or markers, such as ACTH following overnight dexamethasone suppression 4.