Progressive Cerebellar Ataxia After Natalizumab Treatment

A 47-year-old woman with a history of relapsing-remitting multiple sclerosis (MS) receiving natalizumab therapy sought a second opinion regarding a recent diagnosis of secondary progressive disease. She was first diagnosed with multiple sclerosis 8 years earlier. While taking natalizumab, she was monitored for the development of antibodies to JC polyoma virus. Nine months before our evaluation, anti-JC polyoma virus antibodies became positive, with an increased index of 1.1. Given sustained remission, she was continued on natalizumab with increased surveillance and a plan to switch to a different disease-modifying therapy after 24 months. Five months later she noted subacute onset of slurred speech and right upper extremity incoordination. Over the next 4 months she continued to have clinical decline. On examination she had moderate ataxic dysarthria and right greater than left appendicular ataxia. She relied on a wheelchair for transportation and required 1-person assist to stand. Reflexes were brisk with bilateral Babinski sign. This patient with relapsing-remitting multiple sclerosis on natalizumab had a new subacute progressive cerebellar syndrome without radiographic evidence of disease activity. Repeated magnetic resonance imaging showed worsening cerebellar atrophy, right sided greater than left sided, and evolving T2 hyperintensity in the brainstem without enhancement or mass effect. JC polyoma virus polymerase chain reaction was positive. The patient was diagnosed with JC polyoma virus granule cell neuronopathy. Natalizumab was discontinued, and she was treated with 4 of 5 planned cycles of plasma exchange. After her 4th cycle, worsening symptoms developed. Magnetic resonance imaging showed gadolinium enhancement in the brainstem supportive of immune reconstitution inflammatory syndrome. She received high-dose intravenous methylprednisolone followed by a prednisone taper. Her disability progression stabilized. JC polyoma virus central nervous system infection, 1 of several infections reported among treated patients with multiple sclerosis, occurs almost exclusively in immunosuppressed patients, including those receiving disease-modifying therapy for multiple sclerosis.