Post-concussion abnormalities in the m60 somatosensory evoked field recorded by magnetoencephalography

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ObjectiveWe sought to determine whether magnetoencephalography (MEG) might reliably document the presence of neurophysiologic dysfunction after acute concussion. Based on a previous evoked potential study,1 we analysed somatosensory evoked fields (SEFs) elicited by stimulation of the median nerve at the wrist.DesignCase-control study.SettingAcademic tertiary care centre.ParticipantsFive patients with acute concussion (<10 days post-injury); mean age 32±18 yrs, 3 women. 23 age/sex matched controls with no history of concussion.Assessment of risk factorIndependent variable, concussion.Outcome measuresDependent variables, bilateral peak latencies of M20, M30, and M60 SEFs.Main resultsNo differences were found between patients (24 recorded values) and controls (46 recorded values) in M20 (21.7±1.6 ms vs. 22.3±1.5 ms) or M30 (35.4±3.8 ms vs. 33.5±3.3 ms) latencies. M60 latencies were significantly delayed in patients compared to controls (90.4±21.5 ms vs. 64.0±8.6 ms; Mann Whitney U-test, U=186.5, p=0.0001). All symptomatic patients had an abnormally delayed M60 value>2 SDs from the control mean on at least one side. Follow-up patient recordings showed gradual decreases in abnormal M60 latencies over months; weekly MEG and ImPACT testing in one patient showed normalisation of verbal memory at week 2, visual memory and symptom scores at week 5 and M60 latencies at week 10.ConclusionsThe M60 SEF represents the first intracortical stage of neuronal processing of external somatosensory input to the brain. In this preliminary study we found significant differences in M60 latencies between subjects with acute concussion and controls, as well as within subject changes during recovery in the weeks after concussion.Competing interestsNone.

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