Two-year Red Cell Distribution Width–Standard Deviation Change in Multiple Sclerosis Patients Receiving Dimethyl Fumarate Treatment: A Retrospective Analysis

Aim: This study evaluated the relationship between two‑year changes in hematological and inflammatory parameters—including red cell distribution width–standard deviation (RDW‑SD)—and disease progression and treatment response in relapsing‑remitting multiple sclerosis (RRMS) patients receiving dimethyl fumarate (DMF).Materials and Methods: This retrospective study included 58 RRMS patients receiving uninterrupted DMF treatment. Hematological data from two years prior and current values were compared. Parameters analyzed included white blood cell count (WBC), lymphocytes, monocytes, RDW‑SD, and inflammatory indices such as neutrophil/lymphocyte ratio (NLR), monocyte/lymphocyte ratio (MLR), and platelet/lymphocyte ratio (PLR). Normality was assessed by the Kolmogorov–Smirnov test, and paired t‑test, Wilcoxon signed-rank test , and Spearman correlation analyses were applied as appropriate.Results: Significant increases in RDW-SD (p<0.001), NLR (p=0.005), MLR (p=0.003), and PLR (p=0.001) were observed after DMF treatment. Lymphocyte counts decreased significantly (p=0.002). Statistically significant correlations were observed between the change in monocyte count and the Expanded Disability Status Scale (EDSS) score (r=0.386; p=0.003), and between the change in platelet‑to‑monocyte ratio (PMR) and EDSS (r=–0.297; p=0.023). Notably, the increase in RDW‑SD was independent of the conventional RDW-coefficient of variation (CV) (p=0.57).Conclusions: The increase in RDW-SD levels observed during DMF treatment suggests that this parameter may be associated with inflammatory activity. RDW-SD could be evaluated as an auxiliary biomarker in personalized treatment approaches. However, further research is needed to confirm these findings.