Can Low-Level Laser Therapy Have An Impact For Small Fiber Neuropathy?

Kerry Zang, DPM, Janna Kroleski, DPM, Shahram Askari, DPM, and Sanford Kaner, DPM

   A therapy with such promise is low-level laser therapy (LLLT). Researchers have shown that low-level laser therapy promotes: central and peripheral neuron repair; suppression of cyclooxygenase-2 (COX-2); enhancement of peripheral endogenous opioids; upregulation of vascular endothelial growth factor (VEGF); angiogenesis; collagen synthesis and decorin expression during tendon and ligament repair; reduction in fibrosis, suppression of conduction along unmyelinated C fibers; and inhibition of histamine release.28-54

   Low-level laser therapy is an emerging technology to help treat and control pain in the lower extremities. Researchers have shown that low-level laser irradiation can have a positive response for tissues that exhibit microvascular compromise and become anoxic secondary to metabolic injury with resulting microvascular inflammation, oxidative injury, and mitochondrial dysfunction. Authors have demonstrated that the more recently developed 17.5 mW 635 nm laser has a positive response on cell membranes, mitochondria and damaged neurologic structures. Lasers of low intensity initiate analgesic, anti-inflammatory and biostimulatory effects, resulting in an increase in local microcirculation and increased healing.55-57 Increasing microcirculation induces an essential function in the tissue repair process and in pain control. This process allows increases in oxygenation and nutritional supply to tissues. This process allows for the expulsion of metabolic byproducts, which may contribute to pain.

A Closer Look At The Mechanism Of Action Of Low-Level Laser Therapy

Lasers deliver light in a highly concentrated manner defined by a high degree of spatial and temporal coherence. Lasers involve high-intensity photo-bio stimulation of a medium, which can be a gas, liquid, crystal, dye or semiconductor, resulting in the emission of photons.

   The two major categories of laser therapy are class IV and class III, which are differentiated according to output power. Low-level laser therapy is a class III laser and requires only a discrete amount of output intensity or energy (5-500 mW) to yield a clinical response. Power reveals a biphasic dose-response in which higher intensities impede rather than facilitate a cellular and clinical response.58 Low-level lasers operate within the principles of bioorganic photochemistry, a discipline of science that explores the interaction between photons and biochemical pathways in cells.

   The clinical utility of low-level laser therapy is derived from the ability to modulate cellular metabolism and influence a diverse array of intracellular biochemical cascades that directly affect cellular behavior and function.

   The biological effect of coherent laser irradiation on cells is termed photobiomodulation. All light is radiation energy that is measured in discrete units called photons and its effect on cellular components is mediated by biological photo-acceptor molecules that are found in a variety of cellular components throughout the human body.

   Two cellular components in particular that have been identified are cytochrome c oxidase, which is part of the electron transport chain of mitochondria, and porphyrins, which are found in the eukaryotic cell membrane.

   Cytochrome c oxidase is a multi-component membrane protein, which contains a binuclear copper center (CuA) and a heme binuclear center (a3-CuB). Cytochrome c oxidase facilitates the transfer of electrons from cytochrome c to oxygen, driving oxidative phosphorylation.59,60 Researchers believe low-level laser stimulation of cytochrome c oxidase accelerates the transfer rate of electrons and makes more electrons available for the reduction of dioxygen.61-69 Functional changes in the terminal enzyme increase the membrane potential and proton gradient, changing mitochondrial optical properties and increasing the rate of ADP/ATP exchange.70,71

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