Effect of dimethyl fumarate on lymphocyte subsets in patients with relapsing multiple sclerosis.

Abstract

BackgroundIn patients treated with dimethyl fumarate, absolute lymphocyte count decline typically occurs during the first year and then plateaus; early drops have been associated with the development of severe prolonged lymphopenia.ObjectiveWe investigated the effect of dimethyl fumarate on absolute lymphocyte counts and CD4+/CD8+ T cells in patients with relapsing–remitting multiple sclerosis treated with dimethyl fumarate in routine practice.MethodsLymphocyte data were collected via medical chart abstraction. Primary endpoint: change from baseline in absolute lymphocyte count and CD4+/CD8+ counts at 6‐month intervals following dimethyl fumarate initiation.ResultsCharts of 483 patients were abstracted and 476 patients included in the analysis. Mean baseline absolute lymphocyte count (2.23 × 109/l) decreased by ∼39% (95% confidence interval: –41.1 to –37.2) by month 6 and 44% (95% confidence interval: –46.6 to –42.1) by month 12. CD4+ and CD8+ T-cell subsets strongly correlated with absolute lymphocyte count, with greater decreases from baseline to 6 months vs 6–12 months, and in CD8+ vs CD4+ T cells. Prior natalizumab was not a risk factor for lymphopenia.ConclusionDimethyl fumarate-associated decline in absolute lymphocyte count in the first 12 months correlated with decline in CD4+ and CD8+ T cells and was independent of prior natalizumab. Absolute lymphocyte count monitoring continues to be an effective strategy to identify patients at risk of prolonged lymphopenia.