[Corticospinal tract assessment in ALS: transcranial magnetic stimulation]

Results obtained during transcranial magnetic stimulation (TMS) in 79 patients with ALS were compared to those obtained in 10 healthy volunteers. M and F responses evoked by peripheral stimulation of the ulnar and peroneal nerves and then motor evoked potentials (MEP) induced by TMS were recorded in the abductor digiti quinti (AV) and tibial anterior (TA) muscles bilaterally. Central motor conduction time (CMCT) was calculated using MEP and F response latencies. The MEP/M x 100% amplitude ratios were calculated. Mean CMCT was significantly (p < 0.0001) prolonged in patients with ALS (9.6 +/- 4.1 ms for AV and 20.4 +/- 9.6 ms for TA) and MEP/M x 100% amplitude ratios were higher (45 +/- 75% for AV-p < 0.001 and 27 +/- 32.7% for TA p = 0.2). In a sub-group of patients with predominant upper motor neuron (UMN) involvement, the CMCT was significantly prolonged (14.2 +/- 5.8 ms for AV and 28.5 +/- 9.1 ms for TA), but MEP/M x 100% amplitude ratio was 24.1 +/- 37.6% for AV and 11.4 +/- 12.9% TA. These results confirm usefulness of combined analysis of CMCT and MEP/M x 100% amplitude ratio as the method of assessment of pyramidal tract function in ALS.