The effect of spasticity on cortical somatosensory-evoked potentials: changes of cortical somatosensory-evoked potentials after botulinum toxin type A injection.

OBJECTIVE: To evaluate the changes in cortical somatosensory-evoked potentials (SEPs) after botulinum toxin type A injection to determine what effect spasticity has on cortical SEPs.

DESIGN: Intervention study and before-after trial.

SETTING: University-affiliated hospital in Korea.

PARTICIPANTS: Twelve children with spastic hemiplegic cerebral palsy (CP), 7 children with spastic diplegic CP, and 8 patients with traumatic brain injury.

INTERVENTION: All participants had botulinum toxin type A injected into the muscles of the spastic limb.

MAIN OUTCOME MEASURES: SEPs were recorded before and 7 days after the botulinum toxin type A injection. Spasticity of the affected spastic limb was also measured. The short latency and amplitude of waves in SEPs were measured. The SEP results were divided into 3 groups: flat (no evoked potential), abnormal (evoked but delayed in latency), and normal (clear waveform with normal latency).

RESULTS: The normal response of cortical SEP increased after injection. The SEPs exhibited more frequent improvement in the limbs, with greater improvement of spasticity in grade (>1.0 grade) and in patients of younger age (<3y) after injection (P<.05).

CONCLUSION: The observed improvement of cortical SEPs with associated reduction of spasticity that occurred after the botulinum toxin type A injection indicates that spasticity itself can be considered a factor affecting cortical SEPs.