First Adult Case of Echovirus 21–Associated Poliomyelitis-Like Myelitis Presenting with Flaccid Asymmetric Tetraparesis

Background Non-polio enterovirus–associated myelitis is a rare condition causing acute flaccid paralysis due to anterior horn cell injury. While most cases occur in children, reports in adults are exceedingly uncommon. Methods We report the first known case in a 63-year-old woman with relapsed/refractory mantle cell lymphoma (MCL) after second-line therapy with rituximab and ibrutinib. Following leukapheresis for planned CAR-T-cell therapy, she received bridging chemotherapy with bendamustine, cytarabine, and rituximab. During prolonged neutropenia and lymphopenia, she developed sudden asymmetric tetraparesis. Diagnostic workup included brain and spinal MRI, cerebrospinal fluid (CSF) analysis with cytology and flow cytometry, nerve conduction studies (NCS), and electromyography (EMG). Results NCS and EMG demonstrated a predominantly axonal neuropathy with acute denervation. Spinal MRI revealed cervical intramedullary T2 hyperintensities with a characteristic “snake-eye” sign involving the anterior horns. CSF analysis showed normal cell counts and protein levels without lymphoma involvement. Multiplex PCR detected enteroviruses, subsequently identified as Echovirus-21. Initial treatment with intravenous immunoglobulins for suspected Guillain–Barré syndrome was discontinued after confirmation of enterovirus-associated myelitis, and supportive care was provided. Discussion Although rare in adults, enterovirus-associated myelitis should be considered in immunosuppressed patients presenting with acute flaccid paralysis. Early diagnosis using spinal MRI, CSF PCR, and electrodiagnostic studies is essential to avoid misdiagnosis and inappropriate treatment.