Objective
To evaluate the changes of dermatomal SEP (DSEP) in children with a spastic cerebral palsy (CP) after the selective posterior rhizotomy (SPR).

Method
The subjects were 14 spastic CP children, with the age from 3 to 6 years old, who underwent SPR. DSEPs were studied at the L2-3, L4, L5, S1 dermatomes bilaterally, pre and postoperatively. Postoperative DSEPs were interpreted by the changes of latency, amplitude and waveforms.

Results
1) All children were spastic diplegia except one who was a spastic hemiplegia. 2) Preoperative DSEPs were flat or severely distorted in 40 of 112 waveforms (34.5%). 3) Postoperative DSEP latencies were no change in 39.3%, improved in 17.9%, and worsened in 25.6% respectively. Amplitudes were no change in 30.8%, improved in 38.5%, and worsened in 13.7% respectively. Waveforms were no change in 64.1%, improved in 22.2%, and worsened in 8.5% respectively. There was no statistical difference of postoperative changes of the 3 categories according to the root levels.

Conclusion
The results showed that the preoperative DSEPs were abnormal in 34.5% suggestive the lesions of CP being more widespread than strictly involving the motor system. This study confirmed that the most SEPs unchanged by the SPR. A further study for the relationship of postoperative DSEP changes and clinical findings such as functional impairment would be needed.