10/24/14 - A fatal case of progressive multifocal leukoencephalopathy has been reported in a multiple sclerosis patient taking Tecfidera (dimethyl fumarate). Although details of this case are still being disseminated, we believe the patient had not been previously treated with Tysabri or immunosuppressants, making this the first case of PML attributable to Tecfidera. Apparently the patient did have prolonged (>3 years) of lymphopenia (or a very low lymphocyte count), which is a known side effect of the drug. We continue to recommend that patients on Tecfidera have a complete blood count (CBC) checked every six months while taking this medication to screen for lymphopenia. Please discuss this further with your IMSMP physician for additional information or if you have not had a blood test in the last six months.