Predictors of lymphocyte count recovery after dimethyl fumarate-induced lymphopenia in people with multiple sclerosis

Background Dimethyl fumarate (DMF) is an oral drug approved for Relapsing Multiple Sclerosis (RMS) patients. Grade III\r\nlymphopenia is reported in 5–10% DMF-treated patients. Data on lymphocyte count (ALC) recovery after DMF withdrawal\r\nfollowing prolonged lymphopenia are still scarce.\r\nObjectives To characterize ALC recovery and to identify predictors of slower recovery after DMF interruption.\r\nMethods Multicenter data from RMS patients who started DMF and developed lymphopenia during treatment were collected.\r\nIn patients with grade II–III lymphopenia, ALCs were evaluated from DMF withdrawal until reaching lymphocyte\r\ncounts > 800/mm3.\r\nResults Among 1034 patients who started DMF, we found 198 (19.1%) patients with lymphopenia and 65 patients (6.3%)\r\nwho discontinued DMF due to persistent grade II–III lymphopenia. Complete data were available for 51 patients. All patients\r\nrecovered to ALC > 800 cells/mm3 with a median time of 3.4 months. Lower ALCs at DMF suspension (HR 0.98; p = 0.005),\r\nlonger disease duration (HR 1.29; p = 0.014) and prior exposure to MS treatments (HR 0.03; p = 0.025) were found predictive\r\nof delayed ALC recovery.\r\nConclusion ALC recovery after DMF withdrawal is usually rapid, nevertheless it may require longer time in patients with\r\nlower ALC count at DMF interruption, longer disease duration and previous exposure to MS treatments, potentially leading\r\nto delayed initiation of a new therapy.