Somatosensory evoked potentials predict neurolysis outcome in meralgia paraesthetica

Background: The role of somatosensory evoked potentials (SEP) in predicting the outcome of nerve entrapment syndrome following surgical release has not been fully verified. Methods: All patients included in our study had preoperative SEP recordings and had undergone neurolysis for treatment of meralgia paraesthetica by our senior author (KNC) between 1996 and 2000. The outcome of surgery was assessed 6 weeks after the procedure; follow up was continued at 3 month intervals if symptoms persisted. Telephone interviews were conducted to assess long-term results. Univariate and multivariate logistic regression analyses were used to establish the predictive value of side-to-side N1 and P1 latency differences in obtaining complete relief of symptoms following surgery. Results: Twenty-four patients who had preoperative SEP recordings and had undergone neurolysis for meralgia paraesthetica were followed for 4.0 ± 1.5 (SD) years. A prolonged side-to-side N1 latency difference (ΔN1) was found to be significantly associated with complete relief of symptoms at about 6 weeks postoperatively, after adjustment for age, sex and duration of symptoms (OR, 1.75; CI, 1.03-2.96). Logistic regression identified a critical cut-off value of 8 ms (OR, 27.2; CI, 1.4-547.0). This association disappeared with longer follow up. Conclusion: Somatosensory evoked potentials provide significant data for prediction of good surgical outcome for meralgia paraesthetica. Re-evaluation of the diagnosis, adequate trial of conservative treatments and special attention to anomalous branches are recommended for patients with low preoperative ΔN1 values.