Abstract
The mechanism by which laser phototherapy (Low Level Laser Therapy - LLLT) induces analgesia in the treatment of chronic pain is not understood. To investigate a possible role for opioids in this treatment, a double-blind, placebo-controlled study was designed to compare the effect of two dosages (1 J/cm2 and 5 J/cm2) of an infrared (IR) laser (820 nm), a visible red laser (670 nm) and a near-monochromatic light emitting device (660 nm, 30 nm bandwidth) on trigger points. Fifty-six consenting subjects with chronic pain conditions exhibiting myofascial trigger points in the neck and upper trunk region underwent six experimental sessions over a two week period. Blood samples were withdrawn before and after treatment on three of six appointments. Plasma was assayed for β-endorphin (radioimmunoassay, RIA) and adrenocorticotropic hormone (ACTH ∼ two-site immunoradiometric assay, IRMA) to assess opioid response. ACTH was shown to have a cumulative response to treatment with 1 J/cm2 infrared laser (p < 0.001) and 5 J/cm2 red laser (p < 0.05) responding significantly. β-endorphin was noted to be significantly elevated between days one and four (p < 0.05) in subjects who received IR (5 J/cm2) laser. Results indicated that the analgesic response to phototherapy may be mediated through hormonal/opioid mechanisms, and that responses to LLLT are dose and wavelength dependent. A mechanism by which peripheral stimulation using LLLT may elicit activity in the central pathways is proposed.
