Low power He-Ne lasers (λ=632.8nm, 8.5mW, Senkou Med. Mgf. Co., Tokyo) have been used for the treatment of 159 painful out-patients (postherpetic neuralgia 83, herpes zoster 13, whiplash syndrome 9, rheumatoid arthritis 7, reflex sympathetic dystrophy 5, causalgia 5 cases, and etc.) and 12 patients without pain (facial palsy 7 and alopecia areata 5 patients). The effectiveness of the laser therapy in 159 patients is 81.8% by a four-grade evaluation. The degree of pain relief from postherpetic neuralgia is 44.6% after 50 treatments and correlated with the number of treatments. These results suggested that repeated irradiation with low power He-Ne laser is an effective and safe therapy for painful out-patients.
The mechanisms of analgesic effects of low-power laser were categorized into three systems; the first is the reduction of painful stimuli by the antiinflammatory effect, hyperpolarization of neural membrane potentials and the increase in local blood flow after irradiation of lasers, the second is the blocking effect of neural transmission and the third is the inhibition of the dorsal horn neurons. The mechanisms were discussed using results of our basic studies.