The value of dermatomal somatosensory evoked potentials on the evaluation of lumbosacral nerve root decompression during operation

English Keywords:Dermatomal somatosensory evoked potentials  Lumbosacral nerve root  Decompression  Operation  Evaluate

English Abstract:

  【Abstract】 Objectives: To explore the available index and the value of dermatomal somatosensory evoked potentials(DSEP) on the operation of lumbosacral nerve root decompression. Methods: Forty-six cases complained of sensory numbness and diagnosed as unilateral lumbosacral nerve root(L5 or S1) by clinical, magnetic resonance imaging(MRI) and DSEP examination were monitored by DSEP during operation under general anaesthesia form May 2011 to December 2011. There were 34 males and 12 females with a mean age of 41.2 years(range, 20-63 years). 36 cases had L5 nerve root involved, and 10 cases had S1 nerve root . MRI showed intervertebral disc herniation or nerve root canal narrow in all cases. The P40 latency and amplitude of involving nerve root were recorded and compared at pre- and post-decompression after anaesthesia. The free EMG of corresponding segment was monitored as the precaution of nerve root injury during operation(anterior tibial muscle for L5, and gastrocnemius for S1). VAS and ODI scores were used to evaluate the patients′ clinic symptom and neulogical function before and after operation, then the scores were compared. Results: The free EMG showed no iatrogenic injure of nerve root. After decompression, P40 lantency showed extension <0.1 in 32 cases, shortening in 14 cases and shortening >0.1 in 8 cases. The improvement rates of P40 lantency were noted delay in 3 groups: unimproved group(improvement rate ≤0), improved group(00.05). The improvement rate of ODI showed no significant difference among the groups(P>0.05). All the P40 amplitudes of the patients had no loss after decompression. The improvement rate of P40 amplitude was delayed in unimproved group(improvement rate <0.3), improved group(0.3≤improvement rate <0.5) and significant improved group(improvement rate ≥0.5). The improvement rate of VAS in significant improved group was significantly higher than the other groups(P<0.05); and at the follow-up of 6 months, the improvement rate of ODI in the unimproved group was not significant than other groups(P<0.05); and there was no difference between groups with respect to ODI(P>0.05). There were relationships between the improvement rates of P40 amplitude and VAS, as well as course(P<0.05). Conclusions: For cases with short-term typical sensory numbness and diagnosed as unilateral lumbosacral nerve root deficit, the improvement rate of P40 amplitude can be used as index for evaluating the effect of decompression.