Electrophysiological studies of myoclonus in sialidosis type 2.

Electrophysiological investigation was performed in 3 patients with beta-galactosidase and sialidase deficiencies (sialidosis type 2) in order to elucidate the underlying mechanism of intention myoclonus. It is a rare neuronal storage disease that begins in childhood with mental retardation, skeletal abnormalities, progressive myoclonus and cherry-red spots in the macula. Electrophysiological studies showed paroxysmal activities in the EEG, consistent temporal relationship between the EEG spikes and myoclonic jerks demonstrated by jerk-locked averaging, high amplitude somatosensory evoked potentials with altered wave form, and enhanced long-loop reflexes. These results suggest that there is a hyperexcitability of the cerebral cortex, which results in induction of intention myoclonus. The intention myoclonus in sialidosis type 2 is consistent with 'cortical reflex' myoclonus described in progressive myoclonic epilepsy due to various etiologies.