Non-invasive cortical stimulation for drug-resistant pain

Purpose of review Neuromodulation techniques are being increasingly used to alleviate pain and enhance quality of life. Noninvasive cortical stimulation was originally intended to predict the efficacy of invasive (neurosurgical) techniques, but has now gained a place as an analgesic procedure in its own right. Recent findings Repetitive transcranial magnetic stimulation (rTMS): Evidence from 14 randomised, placebo-controlled trials (similar to 750 patients) supports a significant analgesic effect of high-frequency motor cortex rTMS in neuropathic pain. Dorsolateral frontal stimulation has not proven efficacious so far. The posterior operculo-insular cortex is an attractive target but evidence remains insufficient. Short-term efficacy can be achieved with NNT (numbers needed to treat) similar to 2-3, but long-lasting efficacy remains a challenge. Like rTMS, transcranial direct-current stimulation (tDCS) induces activity changes in distributed brain networks and can influence various aspects of pain. Lower cost relative to rTMS, few safety issues and availability of home-based protocols are practical advantages. The limited quality of many published reports lowers the level of evidence, which will remain uncertain until more prospective controlled studies are available. Summary Both rTMS and tDCS act preferentially upon abnormal hyperexcitable states of pain, rather than acute or experimental pain. For both techniques, M1 appears to be the best target for chronic pain relief, and repeated sessions over relatively long periods of time may be required to obtain clinically significant benefits. Patients responsive to tDCS may differ from those improved by rTMS.

Automated summary

Neuromodulation techniques, such as rTMS and tDCS, are being increasingly used to alleviate pain and improve quality of life. Research has shown that rTMS has a significant analgesic effect on neuropathic pain, while tDCS is a lower-cost alternative with fewer safety concerns. However, the limited quality of published reports raises uncertainty about the efficacy of these techniques.