John Cunningham Virus‐induced Cerebellar Granular Cell Neuronopathy in a Patient With MS Treated With Natalizumab

We described a case of John Cunningham virus‐induced granule cell neuronopathy in a 36-year-old patient with multiple sclerosis (MS) who was treated with natalizumab for 6 years. This patient developed progressive cerebellar syndrome. Within 6 months, 3 successive MRIs with DWI disclosed rapidly progressive cerebellar atrophy with cortical cerebellar signal intensity abnormalities, including high signal intensity on DWI with mildly decreased ADC values. This report highlighted the importance of detecting the early MR features of John Cunningham virus neuronopathy in a patient with MS who was treated with natalizumab and who had recent-onset cerebellar syndrome.