[Spinal myoclonus which appeared during the administration of alpha interferon]

We report a 42-year-old man who showed myoclonus in his right leg during alpha-interferon (alpha-IFN) treatment for HCV-RNA positive chronic hepatitis C. The myoclonus continuously persisted even during sleeping. Surface EMG recordings revealed fairly regular about 0.3 Hz periodic grouping discharges synchronized in the right lower extremities muscles. Jerk-locked back averaging method demonstrated a monophasic negative sharp wave associated with the myoclonus. This pre-myoclonus sharp wave was localized on the Cz and preceded the myoclonus by about 60 ms. T 2-weighted gradient-echo MRI images revealed a high-intensity lesion in the right leg motor cortex in the left hemisphere. The myoclonus vanished in association with the disappearance of the above MRI lesion one month after the termination of alpha-IFN therapy. Based on these, we conclude the alpha-IFN may induce the myoclonus in this patient.