Effects of dimethyl fumarate on lymphocyte subsets

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.

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.

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.

Lymphocyte subsets may help to provide better understanding of immunologic and safety impact of DMF.