Abstract
BACKGROUND: Progressive multifocal leukoencephalopathy (PML) has not been reported in pediatric neuromyelitis optica spectrum disorder (NMOSD) and rarely described in children. OBJECTIVES: To report a case of PML in childhood-onset NMOSD. METHODS: A single retrospective case report. RESULTS: Nine years after diagnosis of aquaporin-4 antibody positive NMOSD, a 17-year-old boy treated with rituximab presented with painless right visual loss over 6 weeks coinciding with CD19 repopulation. Acute relapse treatment was given but he continued to deteriorate, and JC virus was detected in cerebrospinal fluid confirming PML. CONCLUSION: PML can occur in childhood-onset NMOSD and protracted clinical presentations with unusual radiological features should prompt JCV testing. Balancing effective immunosuppression while mitigating the risks of associated complications in long-term relapsing conditions remains a challenge.