Simple parameters from complete blood count predict lymphopenia, adverse effects and efficacy in people with MS treated with dimethyl fumarate

Background: Dimethyl fumarate (DMF) is a first-line oral therapy for relapsing-remitting multiple sclerosis (RRMS). This retrospective study aims to determine the utility of routine complete blood counts (CBC) in pre-dicting lymphopenia, adverse effects and efficacy in a real-world clinical setting. Methods: The Calgary Multiple Sclerosis (MS) Clinic manages over 1800 people with MS on disease-modifying therapies (DMT). Data of patients with relapsing-remitting MS (pwMS) who initiated DMF between July 1, 2013 and December 31, 2014 were included. Patients were followed for one year. DMT use is carefully moni-tored and pwMS need a screening CBC and have regular CBCs done at follow-up. Demographic, clinical, MRI and relapse information are collected prospectively in a clinic database. We analyzed CBCs at baseline and month 3. Results: We identified 139 pwMS in the study period who started DMF. Median follow-up time on-drug was 12 (0.16-12) months. In our study, 15.8% of pwMS developed lymphopenia grade 2 or higher. Baseline lymphocyte counts and older age were significant predictors of lymphopenia. Higher baseline eosinophil counts predicted flushing/gastrointestinal adverse effects, and higher baseline monocyte counts were predictive of breakthrough disease activity. Neutrophil and platelet to lymphocyte ratios, markers that have been associated with overall mortality in the general population, were increased at month 3. Conclusions: Routinely obtained CBCs during the screening and monitoring of people with MS starting DMF offer clinically useful information and generate interesting hypotheses. Age and baseline lymphocyte counts are reinforced as clinically useful predictors of lymphopenia. Our novel findings that baseline eosinophil and monocyte counts could offer insights into usual adverse effects and efficacy, respectively, should be further investigated as a potentially new set of biomarkers.