Effects of dimethyl fumarate on lymphocyte subsets.

OBJECTIVE: To evaluate changes in absolute lymphocyte counts, lymphocyte subsets, and infections in patients treated with dimethyl fumarate (DMF) in comparison to the baseline pre-DMF levels. METHODS: A retrospective chart review was conducted of 23 MS patients treated with DMF. Absolute lymphocyte counts and lymphocyte subsets were obtained at baseline and after at least 3 months of DMF treatment. Data on infections requiring medical attention were also collected. RESULTS: A total of 23 patients were included in this analysis, 11 male (48%), 12 female (52%), with a mean age of 44.5±14.1 years, disease duration of 13.7±8.9 years, and EDSS of 3.5±1.7. The time between baseline and treatment lymphocyte counts was 3.9±1.2 months. Significant reductions in absolute lymphocyte counts by 35% (p<0.0001), CD3(+) by 34% (p<0.0001), CD4(+) by 34% (p<0.0001), CD8(+) by 40% (p<0.0001), and CD19(+) counts by 48% (p=0.0098) were found. Grade 2 lymphopenia occurred in 24% of patients and grade 3 lymphopenia occurred in 1 patient. Infections occurred in 26% of patients, mainly as urinary tract infections (22%) and one fatal case of West Nile encephalitis in a patient with grade 3 lymphopenia, who had been on DMF for 5 months. A detailed summary of this fatal case is provided. CONCLUSION: Lymphocyte subsets may help to provide better understanding of immunologic and safety impact of DMF.