Alemtuzumab-related eosinophilic central nervous system vasculitis.

A 36-year-old woman with relapsing remitting multiple sclerosis (MS) presented with right-sided spasms, focal seizures and neuropsychiatric symptoms 10 months after her first course of alemtuzumab. Magnetic resonance imaging (MRI) brain imaging revealed multiple foci of T2 hyperintensity. Subsequent blood and cerebrospinal fluid (CSF) testing for progressive multifocal leukoencephalopathy (PML), vasculitis and infective causes was negative. A brain biopsy was performed, revealing a prominent perivascular inflammatory infiltrate with multiple immune cells including eosinophils, suggesting eosinophilic vasculitis. The patient was treated successfully with cyclophosphamide. The potential sequelae of alemtuzumab treatment are discussed; this treatable complication should be considered when tests for JC virus are negative.