Epilepsy: Marijuana Use Changes Memory Test Results

Physicians attempting to assess cognitive deficits in patients with epilepsy who use marijuana are likely to get inaccurate results on intracarotid amobarbital testing (IAT).

The test is part of a pre-surgical work-up for surgical epilepsy treatment. It involves temporarily inactivating one cerebral hemisphere by the injection of sodium amobarbital to test memory in the other hemisphere.

Reporting at the American Epilepsy Society 69^th Annual Meeting in Philadelphia, PA, Cornelia Dree, MD of the University of Colorado in Denver, CO, and colleagues looked at 58 patients who underwent IAT, of whom 16 patients said they used marijuana at least monthly. Of those, 12 patients reported they used it at least twice a week. During IAT five frequent users had poor memory bilaterally or on the healthy side of the brain.

“Inadequate performance related to marijuana was suspected and led to repeat IAT in three patients after abstinence from marijuana for four weeks,” they wrote. The abstinence period restored sufficient memory function.

“The findings raised concerns that frequent marijuana use may alter IAT results leading to incorrect assessment regarding potential post-operative cognitive deficits,” they concluded. Accordingly, the team’s standard policy has been revised to include asking about marijuana use and telling patients to abstain for four weeks prior to the procedure.

The team said the research was triggered by concerns that marijuana products are becoming more readily available. Its recreational use is legal in Colorado.