Differential Effects of a 5% lidocaine medicated patch in peripheral nerve injury

Introduction: We examined the effect of topical lidocaine on the function of small and large fibers in patients with peripheral neuropathic pain due to traumatic or postoperative nerve injury. Methods: In an open-label study, 24 patients were treated with a 5% lidocaine patch for up to 12 weeks. We recorded contact heat evoked potentials (CHEPs) and performed quantitative sensory testing (QST) before and after treatment with the contralateral side as control. Results: Twenty-one patients (mean age 47.6 +/- 13.5 years) completed the study. Lidocaine increased cold pain threshold (P=0.04) and reduced CHEP amplitude (P=0.007) with no effect on other QST parameters. Patients responding to treatment had less cold detection deficit on the affected side and had a larger increase in cold pain detection threshold following treatment than nonresponders. Conclusions: Controlled trials are warranted to further understand the mechanisms mediating the effects of topical lidocaine.