Myoclonus generators in sialidosis

OBJECTIVE: Sialidosis is an inborn error of metabolism. There is evidence that the myoclonic movements observed in this disorder have a cortical origin, but this mechanism does not fully explain the bilaterally synchronous myoclonus activity frequently observed in many patients. We present evidence of a subcortical basis for synchronous myoclonic phenomena. METHODS: Electromyographic investigations were undertaken in two molecularly and biochemically confirmed patients with sialidosis type-1. RESULTS: The EMG recordings showed clear episodes of bilaterally synchronous myoclonic activity in contralateral homologous muscles. We also observed a high muscular-muscular coherence with near-zero time-lag between these muscles. CONCLUSION: The absence of coherence phase lag between the right-and-left homologous muscles during synchronous events indicates that a unilateral cortical source cannot fully explain the myoclonic activity. There must exist a subcortical mechanism for bilateral synchronization accounting for this phenomenon. SIGNIFICANCE: Understanding this mechanism may illuminate cortical-subcortical relationships in myoclonus.