Electrodiagnostic changes of the lower limbs in subjects with chronic complete cervical spinal cord injury

Objective: To assess the electrodiagnostic changes in the lower limbs as measured by nerve conduction studies (NCSs) and electromyography in individuals with chronic complete tetraplegia, Design: Prospective testing of NCS and electromyography. Setting: Model spinal cord injury rehabilitation center. Participants: Twenty-five individuals with chronic complete tetraplegia without risk factors for peripheral neuropathy or other lower motoneuron disorders. Interventions: Nerve conduction parameters recorded from the peroneal, tibial, and sural nerves, and compared with normal values. The presence of spontaneous activity (SA), including fibrillation and positive sharp waves, recorded in 5 muscle groups-2 proximal (vastus medialis, iliopsoas), 2 distal (tibialis anterior, medial gastrocnemius), and L4 lumbar paraspinals. Analysis to see if the presence of SA correlated with the distance of the muscle from the spinal cord or with spasticity (measured by the modified Ashworth scale). Main Outcome Measures: Nerve conduction latencies and velocities; motor and sensory conduction latencies; compound muscle action potential (CMAP) and sensory nerve action potential amplitudes; spontaneous potentials: fibrillation and positive sharp waves; and spasticity. Results: NCS responses were obtained at a decreased frequency relative to able-bodied subjects. Statistically significant results in comparison to normal means included a diminished sural amplitude, and diminished peroneal and tibial CMAP and nerve conduction velocity (p <.0001). SA was recorded in at least I of the muscles tested in 92% of subjects, with 72% having SA in more than 1 of the muscles tested affected. A significant difference was seen for SA in the medial gastrocnemius as compared with the iliopsoas (p =.039). No correlation was noted in terms of SA with degree of spasticity. Conclusion: A statistically significant difference in NCS responses in the lower limbs in chronic tetraplegia was found relative to normal control values. However, only the frequency of responses elicited and the decreased CMAP of the peroneal nerve are clinically significant. SA was present in many of the lower extremity muscles in the subjects. Predominantly axonal changes were evident in individuals with chronic complete tetraplegia.