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.