Get access

Rhythmic cortical myoclonus in Niemann–Pick disease type C



We here describe a patient with late-infantile Niemann–Pick disease type C (NPC) presenting with worsening myoclonus, seizures, cerebellar symptoms, mild mental impairment, and gaze palsy. Electroencephalographic (EEG) –polymyographic examinations showed abnormally high and diffuse background alpha-activity, enhanced by intermittent photic stimulation. The electromyographic (EMG) showed quasirhythmic myoclonic jerks during motor activation. EEG–EMG frequency analysis (better than jerk-locked back-averaging) demonstrated the cortical origin of the myoclonus. Our observations indicate that cortical myoclonus may occur as the main symptom of NPC. © 2006 Movement Disorder Society