||STUDY DESIGN: Thirty-three patients with single-level,
unilateral lumbosacral radiculopathy underwent micro-decompression and intraoperative
dermatomal evoked potential monitoring. Side-to-side latency asymmetry was
calculated. A criteria for "abnormal" was defined. Intraoperative
dermatomal evoked potentials were obtained before and after decompression.
The changes were correlated with clinical outcome at the 3-month follow-up
examination. OBJECTIVES: To determine whether intraoperative dermatomal
evoked potential latency asymmetry confirms nerve root compression and whether
an improvement of latency asymmetry after decompression predicts a good
clinical outcome. SUMMARY OF BACKGROUND DATA: Intraoperative dermatomal
evoked potential has been proposed as a test to assess the adequacy of nerve
root decompression. Initial reports suggested improvement of dermatomal
evoked potential amplitude and latency after decompression. The clinical
efficacy is controversial because of its technical difficulty and inherent
variation. METHODS: Cervical recording was chosen to reduce the effects
of anesthesia. The asymptomatic nerve root was used as a control. Quality
of the tracings was determined by evoked potentials-to-noise amplitude ratio.
Clinical outcome was based on patient's pain relief and satisfaction. RESULTS:
Tracings of acceptable quality were obtained at baseline in 57.6% (19 of
33) of patients. A side-to-side latency asymmetry > 5% was defined as
abnormal. Before decompression, 68.4% (13 of 19) of patients had an abnormal
dermatomal evoked potential. After decompression, latency asymmetry returned
to normal in every patient. Clinical outcome was good or excellent in 13
patients, fair in four patients, and poor in two patients. Dermatomal evoked
potential latency improvements were not related to variation in clinical
outcome. CONCLUSIONS: Intraoperative dermatomal evoked potential monitoring
is technically demanding. Finding reproducible potentials is difficult.
More research is necessary before general use of dermatomal evoked potentials
for monitoring nerve root decompression.