Red Light Therapy for Neuropathic Pain: Scientific Evidence

Across trials covering 440 participants, a 2016 systematic review and meta-analysis examined non-invasive ways of calming a nerve cluster in the neck as an alternative to injection for neuropathic pain. The review searched 13 research databases and pooled randomized and quasi-randomized trials of therapeutic ultrasound, nerve stimulation, low-level laser therapy, xenon light, and linearly polarized near-infrared light, at wavelengths from 600 to 1600 nm. The review concluded that these non-invasive approaches relieved pain of various causes and were a useful addition to pain management. It also cautioned that the evidence carries a potential risk of bias.

A 3-group design separated patients by how soon treatment began in a 2016 observational study of low-level laser therapy and nerve pain after shingles. 250 patients in Taiwan were grouped into 48 treated within the first 5 days of the rash, 48 treated between days 6 and 14, and 154 who received no light therapy, with treatment using 632.8 nm light at 50 mW and 2 J/cm² for 6 minutes to the band of skin affected. Patients treated within the first 5 days appeared far less likely to develop lasting nerve pain at 1, 3, and 6 months than those given no light therapy. Those treated later showed a lower rate only at the 3-month mark.

This 2013 observational study followed 1 patient whose nerve pain after shingles had lasted 15 years and had resisted every previous treatment. Class 4 laser light at 810 and 980 nm was applied in contact to the upper back, shoulder, and arm at 2 to 4 W and 10 Hz, delivering 600 to 1200 J and 3.5 to 7.1 J/cm² in 10-minute sessions, once a week across 56 days. The report found lower scores on a standard nerve pain questionnaire and on a 0 to 10 pain scale, alongside the complete resolution of the area of skin that hurt to light touch.

3 patients with severe, long-standing nerve pain in an amputation stump took part in a 2012 observational study of low-intensity laser therapy in São Paulo, Brazil. Each had already tried pain medication without much success, and each received 830 nm light at 70 mW and 8 to 15 J/cm² to the stump across 9 sessions given 3 times a week over 21 days. All 3 reported less intense pain and a greater ability to manage daily activities, and that improvement appeared to hold across 4 months of follow-up.

A 2003 randomized controlled trial at a hospital in Minnesota, United States, tested linearly polarized light over a nerve cluster in the neck for arm pain caused by complex regional pain syndrome. 6 adults with normal neurological examinations took part in the first phase, and a second double-blinded phase compared active and placebo light in 12 people, half of whom had the condition, using 600 to 1600 nm light at 920 mW and 88.3 J. 2 of the 6 people with the condition reported their pain more than halved after active treatment. 3 of those 6 also felt warmth during treatment while none of the comparison group did, and the authors concluded that the benefit was suggested rather than proven in this small study but did not depend on changes in nerve-controlled blood vessel tone. The irradiation was well tolerated.

Scores on a standard pain rating scale fell from 6.2 before treatment to 3.6 after 50 sessions in a 1991 clinical trial of helium-neon laser therapy for severe nerve pain following shingles. 18 outpatients in Japan received 632.8 nm light at 8.5 mW for 3 minutes per session, across 50 sessions spread over 243 days. According to the trial, the response rate reached 94.4% by the final session, and the degree of relief rose in step with the number of sessions. No complications were traced to the laser therapy.

Researchers in Japan treated 36 outpatients who had long-standing nerve pain following shingles in a 1989 observational study of helium-neon laser therapy. Each patient received 632.8 nm light at 8 mW to several points around the painful area of skin, in 20 sessions given 2 or 3 times a week across 47 to 70 days. 88.9% of them responded by the end of the 20 sessions, and the average degree of pain relief reached 55.3%, which appeared to rise with the number of sessions given. The report described the treatment as safe as well as effective.

175 of 227 patients who came in with pain improved within 24 hours in a 1985 observational study of laser acupuncture for neuropathic pain, given to 310 patients in a neurosurgery department. Treatment used 830 nm light at 20 to 40 mW and 5 to 50 Hz, applied to Chinese meridian points, local pain points, and the nerves involved in the head and neck, 1 to 7 times a week. The report found that 12 of 39 patients with numbness also improved within a day, and that relief lasted about 2 or 3 days. No side effects were noticed.