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Corticospinal function studied over time following incomplete spinal cord injury
H C Smith1, G Savic, H L Frankel
1Division of Neuroscience & Psychological Medicine, Imperial College School of Medicine, Charing Cross Hospital, London W6 8RF, UK.
Study Design:
Longitudinal.
Objectives:
(1) To perform standard clinical neurological examinations and establish the pattern of clinical change with time following incomplete spinal cord injury (iSCI). (2) To establish the pattern of change in corticospinal electrophysiological function with time after iSCI. (3) To correlate clinical with electrophysiological findings.
Setting:
The National Spinal Injuries Centre, Stoke Mandeville Hospital, Aylesbury, UK and Imperial College School of Medicine, Charing Cross Hospital, London, UK.
Methods:
Neurological assessments and classification were performed according to American Spinal Injuries Association and International Medical Society of Paraplegia (ASIA/IMSOP) standards. Twenty-one patients (ages 18 - 72 years) with iSCI (level C2 - C7, ASIA impairment grades C - D) and 10 healthy control subjects (ages 27 - 57 years) were studied. Electrophysiological tests of corticospinal function were carried out using transcranial magnetic stimulation (TMS) of the motor cortex and electromyographic (EMG) recordings from thenar muscles. Both tests were performed on a number of occasions, beginning 19 - 384 days and ending 124 - 1109 days post-injury, and the group data were pooled into time epochs of 50 or 100 days post-injury for analysis. Seven of the patients were studied on seven or more occasions and were also assessed individually.
Results:
Individual and pooled data indicated that neurological scores improved progressively and tended to stabilise by around 300 days post-injury. When the patients were first assessed, the mean latency for motor evoked potentials (MEPs) and inhibition of voluntary EMG were significantly different from control values. There was no significant change in latency on subsequent sessions for either the grouped or individual patient data. There was no correlation between clinical assessment and electrophysiological data.
Conclusion:
We conclude that the weakened inhibition seen following iSCI is established within a few days of the time of spinal cord trauma. We argue that reduced corticospinal inhibition may be a prerequisite for the recovery of useful motor function.
Sponsorship:
The work was supported by a project grant from The Wellcome Trust.