Risk factors for development of lymphopenia in dimethyl fumarate-treated patients with multiple sclerosis

Background Dimethyl fumarate (DMF, Tecfidera®) is a first-line disease-modifying therapy for relapsing-remitting multiple sclerosis. Lymphopenia is a frequent reason for discontinuation in fumarate-treated patients. Management strategies to minimize risk of lymphopenia are warranted. Objective The aims of this study were to investigate the correlation of body mass index (BMI), baseline absolute lymphocyte count (ALC), age and sex with risk of DMF-induced lymphopenia in MS patients. Methods The study was a retrospective cohort study of 452 MS patients who had been prescribed DMF at six clinics in two Danish regions between May 2014 and September 2017. Data on lymphocyte counts, BMI, age, sex, and reason for discontinuation of DMF were collected through the Danish Multiple Sclerosis Registry, with follow- up to two years after treatment start. Results 28.5% of patients had lymphopenia grade II or higher at some time in the first two years of DMF treatment. Increased risk of lymphopenia was observed in patients with baseline ALC of 1.00–1.49×10 9 cells/L (odds ratio, OR 5.48, p <0.0001) and 1.50–1.99×10 9 cells/L (OR 2.08, p = 0.0009). Reduced risk of lymphopenia was observed in patients with ALC of 2.00–2.49×10 9 cells/L (OR 0.51, p < 0.01) and ≥ 2.50×10 9 cells/L (0.12, p <0.0001). Patients aged ≥ 56 years had an increased risk of lymphopenia (OR 3.58, p <0.001), and patients with BMI ≥ 30 kg/m 2 had a decreased risk of lymphopenia (OR 0.53, p value = 0.03). Conclusion Low baseline ALC and older age were risk factors for DMF-induced lymphopenia, while BMI ≥ 30 kg/m 2 and high baseline ALC were protective factors for developing lymphopenia in MS patients treated with DMF.