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Objective: To report asymptomatic hypereosinophilia as a potential side effect in patients treated with natalizumab, an α-4 integrin blocking agent., Methods: A case series of 3 patients treated with natalizumab for relapsing-remitting multiple sclerosis including functional and phenotypic characterization of their peripheral blood lymphocytes and eosinophils is presented., Results: Marked peripheral blood eosinophilia with more than 2,000 cells/mm(3) emerged in all 3 patients after the fourth natalizumab infusion and was asymptomatic. Hypereosinophilia was associated with enhanced Th2 activity, ceased with drug discontinuation, and in 2 of 3 patients recurred with drug resumption. Despite persistently high eosinophil counts, there were no signs of end-organ damage., Conclusions: Hypereosinophilia may occur during treatment with natalizumab. It seems to reflect enhanced Th2 activity and recedes with systemic corticosteroids. If the patient is asymptomatic, natalizumab may be continued, provided that other causes of eosinophilia are excluded and the patient is carefully monitored.

We describe a patient with acute disseminated encephalomyelitis (ADEM) who was treated with high-dose intravenous methylprednisolone 2 days after onset of neurologic symptoms. Despite poor prognostic factors and extensive white matter lesions, the patient recovered dramatically with no need for maintenance steroid therapy. This case report of fulminant ADEM treated successfully with early high-dose intravenous methylprednisolone, although uncontrolled, suggests that this agent should be studied in other cases.