To evaluate if the number of peripheral lymphocytes of patients with Multiple Sclerosis (MS) is associated with response to DMF after 12 months of treatment.

The optimal response to DMF in MS patients is mediated by a decrease in the inflammatory immune response during disease course. However, predictive biomarkers to assist in decision-making regarding future response to this treatment are lacking.

We evaluated if early clinical and paraclinical variables were likely related with sustained response to DMF after one year of follow-up in a retrospective longitudinal cohort of MS patients who have been under this treatment at some point in the disease course. Disease activity was classified as follows: NEDA, MEDA (Minimal Evidence of Disease Activity). EDA was designated as any existing disease activity greater than MEDA. Appropriate response to treatment was accepted when patients achieved NEDA or MEDA for at least 12 months of follow-up.

From 109 patients who have been treated with DFM, 72 patients (66%) remained under treatment after one year. From them, appropriate response was found in 62 patients (86%). As of different clinical and laboratory variables, the initial reduction in the percentage of peripheral lymphocytes (≥20%) at any point within the first six months of treatment was statistically significantly associated with sustained response after 12 months (AOR: 31.2; CI: 2.24-500; p= 0.01). Besides, patients with disease duration ≤ 8 years were also predisposed to DMF response after one year when compared to patients having a longer disease course (AOR: 8.26; CI: 1.15-58.82; p= 0.03).

Any initial reduction ≥20% in the total lymphocyte count in at least one blood sample drawn within the first six months of DMF treatment was associated with sustained response after 12 months. These results need to be validated in a larger cohort of patients.