Peripheral and Spinal Mechanisms of Pain and Dry Needling Mediated Analgesia: A Clinical Resource Guide for Health Care Professionals

Abstract

There are a number of biochemical, biomechanical, endocrinological and neurovascular mechanisms underpinning the anti-nociceptive and anti-inflammatory effects of dry needling (DN). While myofascial trigger points likely play a role in peripheral pain, a diagnostic tool for localizing them has not been validated, and DN studies that have targeted trigger points to elicit localized twitch responses have reported mixed results. Therefore, the mechanism responsible for DN-mediated analgesia may be more complicated. DN activates opioid-based pain reduction, mediated by endogenous cannabinoids and the sympathetic nervous system, and non- opioid pain relief via serotonin and norepinephrine from the brain stem. DN also triggers the hypothalamic-pituitary-adrenal axis centrally and the corticotropin releasing hormone-proopiomelanocortin-corticosteroid axis locally to inhibit cox-2, reducing inflammatory cytokines. Recent studies demonstrate that DN combined with mechanical and/or electric stimulation may reverse PKC-mediated peripheral hyperalgesic priming by normalizing nociceptive channels, to include TRPV, ASIC, TTX and P2X/Y. Electric DN (EDN) stimulates immune cells, fibroblasts and keratinocytes to release CGRP and substance-P, altering the stimulation of TTX receptors to reverse hyperalgesia. It also encourages the supraoptic nucleus to release oxytocin to quiet ASIC receptors peripherally and stimulate opioid interneurons spinally. Moreover, EDN inhibits ERK1/2 kinase pathways of inflammation in the spinal cord and stimulates Aδ fibers and N/OFQ to reverse C-fiber mediated central changes. Mechanotransduction of fibroblasts and peripheral nerves via TRPV1 and P2X/Y-mediated intracellular Ca2+ wave propagation and subsequent activation of the nucleus accumbens inhibits spinal pain transmission via glycinergic and opioidergic interneurons. The increased ATP is metabolized to adenosine, which activates P1 purinergic receptors, events considered key to DN analgesia and rho kinase-based tissue remodeling. Mechanotransduction-mediated release of histamine further explains analgesia secondary to needling points distal to pain. DN-mediated analgesia is dependent on a number of synergistic physiologic events involving biochemical and mechanical processes in neural, connective and muscle tissue.