Long-lasting involuntary motor activity after spinal cord injury.

STUDY DESIGN: The study design used is prospective cohort study. OBJECTIVES: This study was designed to neurophysiologically characterize spinal motor activity during recovery from spinal cord injury (SCI). SETTING: University of Louisville, Louisville, Kentucky, USA. METHODS: Twenty-five consecutive acute SCI admissions were recruited for this study. The American Spinal Injury Association Impairment Scale (AIS) was used to categorize injury level and severity at onset. Surface EMG recording was carried out initially between the day of admission and 17 days post-onset (6.0 ± 4.3, mean ± s.d. days). Follow-up recordings were performed for up to 9 months after injury. Initial AIS distribution was 7 AIS-A; 3 AIS-B; 2 AIS-C; 13 AIS-D. RESULTS: Twelve subjects (48%) showed long-duration involuntary motor-unit activation during relaxation. This activity was seen on initial examination in nine and on follow-up by 3 months post-injury in three others. It was seen in muscles innervated from the injury zone in 11 and caudal to the lesion in 9 subjects. This activity was independent of the presence or absence of tendon reflexes and the ability to volitionally suppress plantar stimulation elicited reflex withdrawal. CONCLUSION: The form of involuntary activity described here is the likely result of the altered balance of excitation and inhibition reaching spinal motor neurons because of the loss of inhibitory interneurons or their reduced activation by damaged supraspinal drive and the synaptic reorganization that follows SCI. As such, this activity may be useful for monitoring the effects of neuroprotective and restorative intervention strategies in persons with SCI.

Neurophysiological characterization of motor recovery in acute spinal cord injury.

STUDY DESIGN: Prospective cohort study. OBJECTIVE: This study was designed to neurophysiologically characterize motor control recovery after spinal cord injury (SCI). SETTING: University of Louisville, Louisville, Kentucky, USA. MATERIAL: Eleven acute SCI admissions and five non-injured subjects were recruited for this study. METHODS: The American Spinal Injury Association Impairment Scale (AIS) was used to categorize injury level and severity at onset. Multimuscle surface electromyography (sEMG) recording protocol of reflex and volitional motor tasks was initially performed between the day of injury and 11 days post onset (6.4±3.6, mean±s.d. days). Follow-up data were recorded for up to 17 months after injury. Initial AIS distribution was as follows: 4 AIS-A; 2 AIS-C; 5 AIS-D. Multimuscle activation patterns were quantified from the sEMG amplitudes of selected muscles using a vector-based calculation that produces separate values for the magnitude and similarity of SCI test-subject patterns to those of non-injured subjects for each task. RESULTS: In SCI subjects, overall sEMG amplitudes were lower after SCI. Prime mover muscle voluntary recruitment was slower and multimuscle patterns were disrupted by SCI. Recovery occurred in 9 of the 11 subjects, showing an increase in sEMG amplitudes, more rapid prime mover muscle recruitment rates and the progressive normalization of the multimuscle activation patterns. The rate of increase was highly individualized, differing over time by limb and proximal or distal joint within each subject and across the SCI group. CONCLUSIONS: Recovery of voluntary motor function can be quantitatively tracked using neurophysiological methods in the domains of time and multimuscle motor unit activation.