A 27-year-old woman with optic neuritis and cervical myelitis developed hypertrophic demyelinating polyneuropathy. It was hypothesized that the diagnosis was combined central and peripheral demyelination. A hypertrophic nerve was observed subcutaneously, and magnetic resonance imaging demonstrated marked hypertrophy of the nerve roots. The patient was negative for anti-aquaporin 4 antibodies. Her anti-neurofascin 155 antibody levels was slightly elevated, but it was not definitely positive. Pulsed steroid therapy and the administration of immunoglobulin ameliorated her symptoms. Molecules in both the peripheral and central nervous systems might be target antigens, but further investigations will be needed to clarify the precise pathogenic mechanisms.