Lymphopenia during treatment with dimethyl fumarate in patients with multiple sclerosis: Prevalence, predicting factors and clinical outcomes

Background: Lymphopenia is a common side effect of treatment with dimethyl fumarate (DMF) in patients with multiple sclerosis (PwMS). Prevalence and predictive factors of this side effect are still uncertain, because literature has provided discrepant results and it is still a matter of debate if lymphopenia is associated with a better treatment outcome.Methods: We retrospectively recruited PwMS treated for at least one month with DMF and collected clinical, demographic data and absolute lymphocyte count (ALC) during follow-up. Lymphopenia was graded according to CTCAE. Patients according to the grade in lymphopenia (all grades) and severe lymphopenia (grade II-IV). To evaluate predictors of lymphopenia, we compared characteristics of patients with/without lymphopenia and patients with/without severe lymphopenia. A logistic binary regression was performed to elucidate any predictive factor of lymphopenia and severe lymphopenia. Area under the curve (AUC) was calculated to evaluate sensibility and specificity of predictors. We analyzed treatment outcome with NEDA-3 status at 1-and 2-years.Results: 98 of 105 patients treated with DMF were included. 46.9% developed lymphopenia, 27.6% severe lymphopenia. Lymphopenia was associated with basal ALC (p < 0.001, AUC=0.786), treatment duration (p = 0.01, AUC=0.685),% of reduction at third month (p = 0.001, AUC=0.616) Severe lymphopenia was associated with basal ALC (p = 0.003, AUC=0.750).NEDA-3 status at 1-year (n = 66) and at 2-year (n = 44) did not differ in patients with/without lymphopenia (p = 0.059; p = 0.583) or with/without severe lymphopenia (p = 1.02; p = 0.169).Conclusion: Lymphopenia is a common side effect of DMF and basal ALC predicts its development. Lymphopenia is not associated with the achievement of NEDA-3 status.