Characterization of severe action myoclonus in sialidoses

Area of Science:

• Neurology
• Neurophysiology
• Genetics

Background:

• Progressive myoclonus epilepsy (PME) encompasses several genetic disorders.
• Sialidosis is a rare lysosomal storage disease that can cause PME.
• Understanding the specific neurophysiological underpinnings of myoclonus in different PME types is crucial for diagnosis and management.

Purpose of the Study:

• To characterize the severe action myoclonus in patients with PME due to sialidosis.
• To compare neurophysiological findings in sialidosis with those in Unverricht-Lundborg (UL) disease, another PME form.
• To investigate the relationship between neurophysiological markers and myoclonus severity.

Main Methods:

• Assessed EEG-EMG coherence, relative power (RP), and bandwidth (BW) of EMG-peaks in three sialidosis patients and ten UL patients.
• Evaluated somatosensory evoked potentials and long-loop reflexes (LLRs).
• Correlated neurophysiological findings with clinical severity of myoclonus.

Main Results:

• Sialidosis patients exhibited higher EMG-peak RP and narrower BW compared to UL patients.
• EEG-EMG coherence was significantly higher in sialidosis patients.
• Higher coherence and RP, and narrower BW correlated with increased myoclonus severity, with extreme values in sialidosis.
• LLRs in sialidosis patients showed multiple components, reflecting rhythmic jerk recurrence.
• Findings suggest a particularly high level of cortical motor synchronization in sialidosis.

Conclusions:

• Sialidosis-associated PME presents with distinct, severe myoclonus characterized by high cortical motor synchronization.
• Neurophysiological markers like EEG-EMG coherence and EMG-peak characteristics can differentiate PME subtypes.
• These findings highlight the neurophysiological basis for the severe motor impairment in sialidosis.