Risk factors for lymphopenia in patients with relapsing-remitting multiple sclerosis treated with dimethyl fumarate

To identify risk factors for DMF-induced lymphopenia and characterize its impact on T lymphocyte subsets in MS patients. We performed a retrospective analysis of 194 RRMS patients treated with DMF at the Beth Israel Deaconess Medical Center (BIDMC) over a median of 17 months. We reviewed demographics, ethnic background, prior medication history, complete blood counts and T lymphocyte subsets. Possible lymphopenia risk factors examined included age, prior natalizumab exposure, vitamin D levels, and concomitant exposure to carbamazepine, opiates, tobacco, or steroids. Lymphopenia was defined as grade 1: absolute lymphocytes count (ALC) 800–999/μl; grade 2: ALC 500–799/μl; grade 3: ALC 200–499/μl; and grade 4: ALC