[Case of NMO (neuromyelitis optica) spectum disorder triggered by interferon alpha, which involved extensive pyramidal tract lesion of the brain].

A 65-year-old woman developed left optic neuritis during the course of peg-interferon alpha (PEG-IFN-α) and ribavirin combination therapy for chronic hepatitis C. Brain T(2)W-MRI disclosed hyperintense lesions in the corpus callosum and white matter. We diagnosed neuromyelitis optica spectrum disorder (NMOSD) on the basis of anti-aquaporin-4 antibody seropositivity. PEG-IFN-α was discontinued, and she received steroid pulse therapy (intravenous high dose methylprednisolone). Two weeks later she also developed right optic neuritis. Repetitive steroid pulse therapy improved the left optic neuritis, but the upper half of the visual field of the right eye remained impaired. One month later she presented with mild dysarthria and mild left hemiparesis. Brain MRI disclosed an extensive pyramidal tract lesion from the right corona radiata to the pedunculus cerebri. This cerebral pyramidal tract lesion is associated with NMOSD. Our case corresponds to the past reports of optic neuritis or multiple sclerosis-like disease triggered by IFN-α. IFN-α may trigger NMOSD via a biological effect characteristic of Type I IFNs, a group that includes IFN-α and IFN-β.