Natalizumab induced blood eosinophilia: A retrospective pharmacovigilance cohort study and review of the literature.

OBJECTIVE To describe frequency of natalizumab related eosinophilia and clinical symptoms of eosinophilic disease in our monocentric cohort. METHODS Comparison of clinical characteristics of 115 natalizumab treated and 116 untreated RRMS patients and review of literature. RESULTS 38% of natalizumab treated patients had eosinophilia, which occurred significantly more frequently compared to untreated MS patients (3%, p-value<0.001). In symptomatic patients, mean eosinophil counts were significantly higher than in asymptomatic patients and symptoms developed within one year. DISCUSSION Eosinophilia is a side effect of natalizumab and mostly asymptomatic. However, few patients develop within one year after start of natalizumab an eosinophilic disease as severe side effect.