Hematologic modifications in natalizumab-treated multiple sclerosis patients: An 18-month longitudinal study

OBJECTIVE: To monitor the hematologic modifications in the peripheral blood of patients with relapsing-remitting multiple sclerosis treated with natalizumab. METHODS: The cohort included 44 patients with relapsing-remitting multiple sclerosis treated monthly with natalizumab for 18 months. Peripheral blood was collected before treatment initiation and on a monthly basis during the treatment course. Complete blood cell count was performed using automated hematology systems. Blood smears were prepared and analyzed when abnormal values were detected. RESULTS: Mean total white blood cell, lymphocyte, and eosinophil counts were significantly higher 1 month after treatment initiation and remained stable during the 18 months of follow-up. Monocyte counts increased progressively during the 18-month treatment with natalizumab. Erythroblasts and neutrophil precursors were absent before treatment initiation but were present in 16% and 6.8% of patients, respectively, 1 month after the first natalizumab infusion. The proportion of patients with erythroblasts and neutrophil precursors remained stable throughout the 18-month follow-up period. On an individual patient basis, a fluctuating level of erythroblasts and neutrophil precursors was observed. No difference in mean erythrocyte, hemoglobin, hematocrit, thrombocyte, and neutrophil levels was observed before and after 18 months of natalizumab treatment. No cases of myelodysplastic syndrome or acute leukemia were observed. CONCLUSION: Chronic treatment with natalizumab is associated with significant modifications in complete blood cell count, including emergence of hematopoietic precursors that are not present in peripheral blood under normal conditions. None of these modifications were associated with malignancy.