Motor evoked potentials recorded from muscles versus nerves after lumbar stimulation in healthy subjects and patients with disc-root conflicts

Objective: The study aimed to describe properties and to prove diagnostic usefulness of motor evoked potentials (MEPs) recordings from muscles versus nerves of lower extremities when induced at lumbar levels with magnetic field. Methods: Methodologically similar MEPs recordings from muscles and nerves of lower extremities were performed once in healthy volunteers (N = 43) and patients with disc-root conflicts at lumbar spine levels (N = 43, proven in MRI studies). Simultaneous electroneurographic (ENG) recordings following stimulation of peroneal nerves verified neural impulses transmission in motor fibers peripherally and at L5 ventral roots. Results: ENG studies in patients proven only moderate axonal type of peroneal nerves injury. The mean values of MEPs amplitudes recorded from nerves were significantly different from those recorded in anatomically related muscles, both in controls (1179.6 +/- 451.2 vs 1718.3 +/- 481.3) and patients (495.6 +/- 275.9 vs 1218.2 +/- 465.5) (p = 0.0009-0.0000012); they are about 30% and 51% smaller, respectively. In both groups of subjects, latencies of MEPs recorded from nerves were shorter at about 3.0 ms and characterized by a slightly longer duration (3.0-5.0 ms) than those recorded from muscles. Results revealed positive correlations between decrease of amplitudes in sEMG and MEPs recordings from lower extremities muscles indicating consequences of pathology in neural transmission from spinal centers. Conclusions: Results of this study point to clear-cut characteristics of MEPs induced oververtebrally with the magnetic field in parameters recorded in healthy subjects and patients with consequences of chronic L4-L5 low back pain, which can be easily implemented in clinical practice. Non-invasive method of MEPs recorded from nerves can be helpful for diagnosing of patients with visible atrophic changes in muscles and simultaneous symptoms of only slight pathology in transmission of nerve impulses peripherally.