title: Giant early components of somatosensory evoked potentials to tibial nerve stimulation in cortical myoclonus.
abstract: Enlarged cortical components of somatosensory evoked potentials (giant SEPs) recorded by electroencephalography (EEG) and abnormal somatosensory evoked magnetic fields (SEFs) recorded by magnetoencephalography (MEG) are observed in the majority of patients with cortical myoclonus (CM). Studies on simultaneous recordings of SEPs and SEFs showed that generator mechanism of giant SEPs involves both primary sensory and motor cortices. However the generator sources of giant SEPs have not been fully understood as only one report describes clearly giant SEPs following lower limb stimulation. In our study we performed a combined EEG-MEG recording on responses elicited by electric median and tibial nerve stimulation in a patient who developed consequently to methyl bromide intoxication CM with giant SEPs to median and tibial nerve stimuli. SEPs wave shapes were identified on the basis of polarity-latency components (e.g. P15-N20-P25) as defined by earlier studies and guidelines. At EEG recording, the SEP giant component did not appear in the latency range of the first cortical component for median nerve SEP (N20), but appeared instead in the range of the P37 tibial nerve SEP, which is currently identified as the first cortical component elicited by tibial nerve stimuli. Our MEG and EEG SEPs recordings also showed that components in the latency range of P37 were preceded by other cortical components. These findings suggest that lower limb P37 does not correspond to upper limb N20. MEG results confirmed that giant SEFs are the second component from both tibial (N43m-P43m) and median (N27m-P27m) nerve stimulation. MEG dipolar sources of these giant components were located in the primary sensory and motor area.
authors.affiliation: Department of Neuroscience, Imaging and Clinical Sciences, "G. d'Annunzio" University and Aging Research Centre, Ce.S.I., "G. d'Annunzio" University Foundation, Chieti, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Anzellotti
authors.affiliation: Department of Neuroscience, Imaging and Clinical Sciences, "G. d'Annunzio" University and Aging Research Centre, Ce.S.I., "G. d'Annunzio" University Foundation, Chieti, Italy; Department of Neurology, SS Annunziata Hospital, Chieti, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Onofrj
authors.affiliation: Department of Neuroscience, Imaging and Clinical Sciences, "G. d'Annunzio" University and Aging Research Centre, Ce.S.I., "G. d'Annunzio" University Foundation, Chieti, Italy; Department of Neurology, SS Annunziata Hospital, Chieti, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Bonanni
authors.affiliation: Department of Neuroscience, Imaging and Clinical Sciences, "G. d'Annunzio" University and Aging Research Centre, Ce.S.I., "G. d'Annunzio" University Foundation, Chieti, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Saracino
authors.affiliation: Department of Neurology, SS Annunziata Hospital, Chieti, Italy; ITAB, "G. d'Annunzio" University Foundation, Chieti, Italy.
authors.forename: Raffaella
authors.initials: R
authors.lastname: Franciotti
mesh_terms: D000328:Adult; D002540:Cerebral Cortex / Q000503:physiopathology*; D004558:Electric Stimulation; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D015225:Magnetoencephalography; D008475:Median Nerve / Q000503:physiopathology; D009207:Myoclonus / Q000503:physiopathology*; D013979:Tibial Nerve / Q000503:physiopathology*
keywords: Cortical myoclonus; Magnetoencephalography; Motor cortex; Somatosensory evoked field; Somatosensory evoked potential; Tibial nerve stimulation