TEP propagation in early RRMS patients and controls; A TMS-EEG study

Aim:

The aim of this study was to measure effective cortico-cortical connectivity in Multiple sclerosis (MS) patients by TMS-evoked potential (TEP) latencies evoked by transcranial magnetic stimulation (TMS) of the hand area of the primary motor cortex of one hemisphere and recording of TEPs at the homologue site in the non-stimulated contralateral hemisphere. Both interhemispheric directions were tested. Interhemispheric latencies of the two main reproducible TEPs [1], the positive component at 60 ms and the negative component at 100 ms (P60 and N100, respectively), were expected to be significantly prolonged in MS compared to healthy volunteers.

Method:

The study compared interhemispheric propagation of P60 and N100 in groups of 12 patients with early-stage relapse-remitting MS (RRMS) and 16 age- and gender-matched healthy controls. TEPs were recorded by means of TMS-EEG and their latencies were statistically evaluated in 10 channels around the stimulation site and in 10 corresponding electrodes in the non-stimulated contralateral hemisphere. Interhemispheric conduction time was calculated by the difference of TEP latency in non-stimulated vs. stimulated hemisphere.

Results:

A 2 × 2 ANOVA on interhemispheric conduction time showed a significant prolongation for the N100 from left to right hemisphere in MS compared to controls, while no group differences were found for the P60 and the N100 from right to left hemisphere.

Conclusion:

The results provide first evidence that the N100 may constitute an interesting marker to measure interhemispheric conduction delays in early-stage RRMS. The specificity of the present finding and its relation to fiber tract pathology will be examined in further correlative analysis with diffusion tensor imaging and other structural MRI data

1. Lioumis, P., et al., Reproducibility of TMS-Evoked EEG responses. Hum Brain Mapp, 2009. 30(4): p. 1387 – 96.