Predictability of adequacy of spinal root decompression using evoked potentials.

Dermatomal evoked potentials are being used to obtain accurate information concerning the viability of specific nerve root pathways and the quality and extent of nerve root decompression. Twelve patients with quantifiable weakness were selected and tested before, during, and after surgery. Nine patients showed dramatic intraoperative electrical improvement, including decreased latencies and/or increased amplitudes; all had postoperative relief of pain and motor return. Three patients showed variable intraoperative electrical responses with complete pain relief but no motor improvement. No patients had false-negative findings. Intraoperative monitoring of dermatomal evoked potentials appears to be of value in predicting the quality of spinal decompression. Similar monitoring of somatosensory evoked potentials alone cannot provide the specificity for individual root levels that is available by monitoring individual dermatomes.