Noninvasive Brain Stimulation for Cancer Pain Management in Nonbrain Malignancy: A Meta-Analysis

Purpose. Noninvasive brain stimulation (NIBS) has been reported to have analgesic effects on fibromyalgia and chronic neuropathic pain; however, its effects on cancer pain have yet to be determined. The present study aimed to evaluate the effects of NIBS on patients with pain secondary to nonbrain malignancy. Methods. Electronic databases including PubMed, Embase, Cochrane Library, and Web of Science were searched from inception through June 5th, 2022. Parallel, randomized, placebo-controlled studies were included that enrolled adult patients with cancer pain, except for that caused by brain tumors, compared NIBS with placebo stimulation, and reported sufficient data for performing meta-analysis. Results. Four parallel, randomized, sham-controlled studies were included: two of repetitive transcranial magnetic stimulation (rTMS), one of transcranial direct current stimulation (tDCS), and one of cranial electrical stimulation (CES). rTMS significantly improved pain in the subgroup analysis (standardized mean difference (SMD): -1.148, 95% confidence interval (CI): -1.660 to -0.637, (p < 0.001)), while NIBS was not benefited in reducing pain intensity (SMD: -0.632, 95% CI: -1.356 to 0.092, p = 0.087). Also, NIBS significantly improved depressive symptoms (SMD: -0.665, 95% CI: -1.178 to -0.153, p = 0.011), especially in the form of rTMS (SMD: -0.875, 95% CI: -1.356 to -0.395, p < 0.001) and tDCS (SMD: -1.082, 95% CI: -1.746 to -0.418, p = 0.001). Conclusion. rTMS significantly improved pain secondary to nonbrain malignancy apart from other forms of NIBS without major adverse events.