[Normal values and age-related changes in magneto-electric evoked compound muscle potentials]

A number of 57 normal subjects was investigated using transcranial magnetic stimulation of the motor cortex and transcutaneous magnetic stimulation of the spinal nerve root in order to obtain normative data for central and peripheral motor latencies. Under standardized conditions (site of stimulation, stimulus intensity, degree of voluntary tonic background activation) muscle compound action potentials were recorded from different muscles of the upper and lower extremity: M. biceps brachii, M. extensor carpi radialis, M. interosseus dorsalis I, M. vastus medialis, M. tibialis anterior, and M. extensor digitorum brevis. Onset latency, peak to peak amplitude (% of maximal M-wave), duration and configuration of the muscle compound action potentials were evaluated (Fig. 1 and Tab. 1-6). Central and peripheral motor latencies were determined by stimulation over two different points of the neuraxis (cortex/cervical or lumbar nerve roots). Central motor latencies were calculated by subtracting the peripheral conduction time from the onset latency of the fastest cortically evoked muscle response. Not only the peripheral but also the central motor latencies were found to increase in higher ages (Tab. 6). This has to be taken into account when elderly patients are examined for diagnosis of disorders of the descending motor tracts.