Natalizumab-induced progressive multifocal leukoencephalopathy.

A 55-year-old woman with known relapsing-remitting multiple sclerosis (RRMS) on natalizumab (Tysabri®) for 3 years was admitted to the hospital with worsening word-finding difficulties and gait instability. Neurologic examination revealed right hemianopia, right arm hemiplegia, right-sided sensory loss, and global aphasia. The patient underwent MRI and PET imaging with concurrent electroencephalogram. She was subsequently diagnosed with natalizumab-induced progressive multifocal leukoencephalopathy (PML) and treated with plasmapheresis, intravenous immunoglobulin, and high-dose intravenous steroids. Steroids were continued over a 3-month hospital course and tapered upon discharge. Speech, arm strength, and ambulation have since improved.