Abstracts

Rationale: Sialidosis is a rare lysosomal storage disorder resulting from α-N-acetylneuraminidase deficiency. Clinically, one of the most characteristic presentations with this autosomal recessive disorder is intractable myoclonic seizures. Currently, however, little is known about the electrographic (EEG) features associated with this rare disease Methods: Observation of electrographic (EEG) features in fraternal twins afflicted with sialidosis during their clinic visits and hospital admissions from childhood to adulthood of both Results: These 27 year old fraternal twins, brother and a sister, were both diagnosed with sialidosis and had been followed in neurology outpatient clinics and during many hospital admissions since their early childhood. Both patients presented with intractable myoclonic seizures, ataxia, tremor, spasticity and progressive cognitive decline. Cherry-red spots were identified in both patients. Both had routine EEGs and the brother also had multiple long-term video EEG monitoring studies during several prolonged hospitalizations prior to his death secondary to intractable seizures and multiple medical complications. In both patients, the interictal EEG records were characterized by continuous generalized high frequency background with waxing and waning low amplitude. Intermittently, clusters of repetitive generalized polyspikes evolved from such a background. Comparing to the background activities, the polyspikes had mildly increased amplitude and with little change of the high frequency. Their morphologies were uniform with stereotyped comb-looking waveforms, which were identical in both patients. In the brother, the duration of repetitive discharges was more frequent and prolonged than his twin sister. In addition, repetitive EEG seizures were also identified by the prolongation of these generalized epileptiform discharges into sustained segments in a stereotyped pattern. Those EEG seizures were found to be correlated with generalized, stereotyed myoclonus. Closer to his death, the EEG and clinical seizures became almost continuous despite aggressive treatments in the brother Conclusions: To our knowledge this is the first case series documenting such stereotyped EEG findings in fraternal twins afflicted with sialidoss. Our findings are in general consistent with a previous observation. These findings suggest that the sustained and stereotyped diffuse high frequency discharges are characteristic for sialidosis. The transition of such as background pattern into more uniformed and repetitive polyspikes appears to indicate disease progression. The nearly identical high frequency interictal and ictal discharges may be a signature finding with sialidosis. The pathophysiological mechanism(s) underlying these characteristic EEG changes needs to be investigated to enable assistance with clinical diagnosis and management of these patients