Background and Objective
Highly variable pain mechanisms in people with low back pain or spine-related leg pain might contribute to inefficacy of neuropathic pain medication. This meta-analysis aimed to determine how neuropathic pain is identified in clinical trials for people taking neuropathic pain medication for low back pain or spine-related leg pain and whether subgrouping based on the presence of neuropathic pain influences efficacy.
Methods
EMBASE, MEDLINE, Cochrane Central, CINAHL [EBSCO], APA PsycINFO, ClinicalTrials.gov, and the World Health Organization International Clinical Trials Registry were searched from inception to 14 May, 2024. Randomized and crossover trials comparing first-line neuropathic pain medication for people with low back pain or spine-related leg pain to placebo or usual care were included. Two independent authors extracted data. Random-effects meta-analyses of all studies combined, and pre-planned subgroup meta analyses based on the certainty of neuropathic pain (according to the neuropathic pain Special Interest Group [NeuPSIG] neuropathic pain grading criteria) were completed. Certainty of evidence was judged using the grading of recommendations assessment development and evaluation [GRADE] framework.
Results
Twenty-seven included studies reported on 3619 participants. Overall, 33% of studies were judged unlikely to include people with neuropathic pain, 26% remained unclear. Only 41% identified people with possible, probable, or definite neuropathic pain. For pain, general analyses revealed only small effects at short term (mean difference [MD] − 9.30 [95% confidence interval [CI] − 13.71, − 4.88], I2 = 87%) and medium term (MD − 5.49 [95% CI − 7.24, − 3.74], I2 = 0%). Subgrouping at short term revealed studies including people with definite or probable neuropathic pain showed larger effects on pain (definite; MD − 16.65 [95% CI − 35.95, 2.65], I2 = 84%; probable; MD − 10.45 [95% CI − 14.79, − 6.12], I2 =20%) than studies including people with possible (MD − 5.50 [95% CI − 20.52, 9.52], I2 = 78%), unlikely (MD − 6.67 [95% CI − 10.58, 2.76], I2 = 0%), or unclear neuropathic pain (MD − 8.93 [95% CI − 20.57, 2.71], I2 = 96%). Similarly, general analyses revealed negligible effects on disability at short term (MD − 3.35 [95% CI − 9.00, 2.29], I2 = 93%) and medium term (MD − 4.06 [95% CI − 5.63, − 2.48], I2 = 0%). Sub-grouping at short term revealed larger effects in studies including people with definite/probable neuropathic pain (MD − 9.25 [95% CI − 12.59, − 5.90], I2 = 2%) compared with those with possible/unclear/unlikely neuropathic pain (MD −1.57 [95% CI − 8.96, 5.82] I2 = 95%). Medium-term outcomes showed a similar trend, but were limited by low numbers of studies. Certainty of evidence was low to very low for all outcomes.
Conclusions
Most studies using neuropathic pain medication for low back pain or spine-related leg pain fail to adequately consider the presence of neuropathic pain. Meta-analyses suggest neuropathic pain medication may be most effective in people with low back pain or spine-related leg pain with a definite/probable neuropathic pain component. However, the low to very low certainty of evidence and poor identification of neuropathic pain in most studies prevent firm recommendations.