Study design: Case-control study.
Objective: To investigate the number of motor units from the tibialis anterior (TA) muscle in normal subject and its change after SCI.
Setting: China Rehabilitation Research Center, Beijing, China.
Methods: Motor unit number estimation (MUNE) in 45 control subjects (35 young subjects with an average age of 36 years, and 10 elderly subjects with an average age of 65 years) was performed by using adapted multiple point stimulation method (AMPS). Twenty patients with SCI (10 subacute patients with an average age of 39 years, and 10 chronic patients with an average age of 34 years) were also examined for three times in 3 months with the same method.
Results: The mean MUNE value of the TA muscle was 188+/-20 in the control group, and 40+/-33 in subacute SCI patients (P<0.01 vs young controls). A continuous increase in the MUNE value was observed in subacute SCI patients during the later follow-up period. In the chronic SCI group, the mean MUNE value was 173+/-29 which was similar to that of young control group.
Conclusions: AMPS could be a useful procedure for quantifying changes of MUNE values after SCI. Changes in functional motor unit number may occur distal to the site of lesion in SCI patients. These phenomena may be caused by neuronal plasticity in motor units, reversible transsynaptic degeneration and/or local functional depression. Owing to the limited sample size and a wide age range of subjects recruited in this study, future study are warranted for revealing detailed changes of MUNE parameters after SCI and exploring the underlying mechanisms.