Abstract
In progressive myoclonic epilepsy (PME), a rare epileptic syndrome caused by a variety of genetic disorders, the combination of peripheral stimulation and functional magnetic resonance imaging (fMRI) can shed light on the mechanisms underlying cortical dysfunction. The aim of the study is to investigate sensorimotor network modifications in PME by assessing the relationship between neurophysiological findings and blood oxygen level dependent (BOLD) activation. Somatosensory-evoked potential (SSEP) obtained briefly before fMRI and BOLD activation during median-nerve electrical stimulation were recorded in four subjects with typical PME phenotype and compared with normative data. Giant scalp SSEPs with enlarger N20-P25 complex compared to normal data (mean amplitude of 26.2 ± 8.2 μV after right stimulation and 27.9 ± 3.7 μV after left stimulation) were detected. Statistical group analysis showed a reduced BOLD activation in response to median nerve stimulation in PMEs compared to controls over the sensorimotor (SM) areas and an increased response over subcortical regions (p < 0.01, Z > 2.3, corrected). PMEs show dissociation between neurophysiological and BOLD findings of SSEPs (giant SSEP with reduced BOLD activation over SM). A direct pathway connecting a highly restricted area of the somatosensory cortex with the thalamus can be hypothesized to support the higher excitability of these areas.
Highlights
Progressive myoclonic epilepsies (PMEs) are a group of rare genetic disorders with geographical and ethnic variations, characterized by worsening myoclonus, generalized seizures, and progressive neurological deterioration including cerebellar dysfunction and dementia
PMEs differ from juvenile myoclonic epilepsy on the following aspects: i) complex phenotype including epilepsy plus movement disorder; ii) progressive neurological disability; iii) failure to respond to antiepileptic drugs; iv) slowing of background electroencephalographic (EEG) activity[2]; v) presence of giant evoked potentials[3]
The extent of cortical areas activated in PME subjects was overall reduced compared to controls
Summary
Progressive myoclonic epilepsies (PMEs) are a group of rare genetic disorders with geographical and ethnic variations, characterized by worsening myoclonus, generalized seizures, and progressive neurological deterioration including cerebellar dysfunction and dementia. PMEs differ from juvenile myoclonic epilepsy on the following aspects: i) complex phenotype including epilepsy plus movement disorder (action myoclonus); ii) progressive neurological disability; iii) failure to respond to antiepileptic drugs; iv) slowing of background electroencephalographic (EEG) activity[2]; v) presence of giant evoked potentials[3]. The PMEs core phenotype results from different diseases that have heterogeneous genetic backgrounds, the most frequent being Unverricht-Lundborg disease (ULD), Lafora disease (LD), and other rarer pathologies[4]. In PMEs, myoclonus has a cortical correlate disclosed by the analysis of EEG-electromyography (EMG) coupling, with a time-locking of myoclonic muscle contraction and spikes on EEG. Other signs of cortical hyper-excitability include somatosensory evoked potentials (SSEPs) of increased amplitude, known as giant-evoked potentials
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