Electrophysiological evaluation of motor pathways to proximal lower limb muscles: A combined method and reference values

Abstract

Objective In contrast with their important functional and clinical role, motor pathways to proximal muscles of lower limbs are rarely investigated in clinical neurophysiology. We describe a method to evaluate central and peripheral pathways to these muscles and report reference values. Methods Recording of both quadriceps was performed in 100 subjects. We analyzed the maximal M response after electrical stimulation of the femoral nerve, the patellar T reflex and the motor evoked potential (MEP) after transcranial magnetic stimulation. We defined the central motor conduction time as the difference between the MEP latency and the peripheral motor conduction time, estimated as the half of the T latency minus 0.5 ms. Results The mean MEP latency is 20.6 ms (SD 1.99 ms), central motor conduction time 10.1 ms (SD 1.29 ms), MEP/M amplitude ratio 60.0% (SD 15.75%). Normal limits according to height and age are provided for each parameter and for interside asymmetry. Conclusions This method to investigate the central and peripheral motor pathways supplying the L2–L4 myotomes is simple, painless and rapidly performed. The T reflex provides additional information on the proximal sensory pathways. Significance This method will be useful in many clinical conditions.