Effect of 1.5% Topical Diclofenac on Clinical Neuropathic Pain.

Ahmed, Shihab U; Zhang, Yi; Chen, Lucy; Cohen, Abigail; St Hillary, Kristin; Vo, Trang; Houghton, Mary; Mao, Jianren

BACKGROUND Neuropathic pain is a condition resulting from injury to the peripheral and/or central nervous system. Despite extensive research over the last several decades, neuropathic pain remains difficult to manage. METHODS The authors conducted a randomized, placebo-controlled, double-blinded, and crossover clinical trial to examine the effect of 1.5% topical diclofenac (TD) on neuropathic pain. The authors hypothesized that 1.5% TD would reduce the visual pain score and improve both quantitative sensory testing and functional status in subjects with neuropathic pain. The authors recruited subjects with postherpetic neuralgia and complex regional pain syndrome. The primary outcome was subject's visual pain score. RESULTS Twenty-eight subjects completed the study (12 male and 16 female) with the mean age of 48.8 yr. After 2 weeks of topical application, subjects in 1.5% TD group showed lower overall visual pain score compared with placebo group (4.9 [1.9] vs. 5.6 [2.1], difference: 0.8; 95% CI, 0.1 to 1.3; P = 0.04) as well as decreased burning pain (2.9 [2.6] vs. 4.3 [2.8], difference, 1.4; 95% CI, 0.2 to 2.6; P = 0.01). There were no statistical differences in constant pain, shooting pain, or hypersensitivity over the painful area between the groups. This self-reported improvement of pain was corroborated by the decreased pain summation detected by quantitative sensory testing. There were no statistically significant changes in functional status in these subjects. There were no complications in both groups. CONCLUSION The findings indicate that 1.5% TD may serve as an effective treatment option for patients with neuropathic pain from postherpetic neuralgia and complex regional pain syndrome.