Phil Harrington, DC, CMLSO, FASLMS

Peripheral neuropathy is a general term for a series of disorders that result from damage to the peripheral nervous system. Peripheral neuropathy can affect multiple nerves (polyneuropathy) or single nerves (mononeuropathy). Mononeuropathy is usually damage to a single nerve or nerve group by trauma, injury, local compression, prolonged pressure, or inflammation. Examples include carpal tunnel syndrome and Bell’s Palsy.[i]

Polyneuropathies are more common, and are caused by diabetes, chemotherapy, toxic chemical exposure, chronic alcoholism, certain medications and more[ii]. This article will focus on lower extremity peripheral neuropathy caused by diabetes and chemotherapy, and how photobiomodulation (PBM, commonly known as laser therapy) with a class 4 therapeutic laser is a safe, non-invasive yet very effective treatment solution.

Peripheral neuropathy (PN) is a polyneuropathy caused by diabetes, chemotherapy, toxic chemical exposure, chronic alcoholism, certain medications and more[iii]. Medical treatments for neuropathy include opioid pain medications which have high potential for addiction and abuse. Photobiomodulation (PBM, also known as laser therapy) with a class 4 therapeutic laser is a non-invasive, safe and very effective treatment solution for PN.

The number of people with diabetes worldwide is predicted to double between 2000 and 2030, approaching a pandemic level of 366 million people. Diabetic peripheral neuropathy has a lifetime prevalence of approximately 50% and is a leading cause for disability due to foot ulceration and amputation, gait disturbance, and fall-related injury. Roughly 30% of patients suffer from neuropathic pain.[iv]

In 2015, roughly 30.3 million people, or 9.4% of the US population suffer from diabetes, with about one-fourth of those being undiagnosed. Average medical expenditures for people with diagnosed diabetes were about $13,700 per year.[v] Diabetic peripheral neuropathy signs and symptoms include numbness, loss of temperature sensation, tingling or burning, and more.[vi]

Chemotherapy-induced peripheral neuropathy (CIPN) is a common side-effect of anti-neoplastic pharmaceuticals. It typically manifests as numbness, paresthesia, pain, and/or burning. Motor dysfunction and/or autonomic dysfunction can also occur. The prevalence of CIPN after chemotherapy is 20–51%, but estimates vary considerably depending on the severity threshold and mechanism of detection. Underreporting of both the prevalence and magnitude of CIPN is likely because sensory symptoms are not always apparent.[vii]

In vitro and in vivo animal experiments show that PBM with infrared laser light can modulate neuropathic pain by altering chronic inflammation, decreasing mechanical allodynia, suppressing conduction velocity and reducing amplitude of action potentials.[viii] Further animal experiments show that PBM-induced anti-nociception comes from the release of central opioids, helping with pain relief in the early stages of treatment. Later stages of PBM treatment appear to be inducing permanent neuroplastic changes that maintain the antinociceptive state, without depending on opioid release in the periphery.[ix]

The general mechanisms of action for PBM are numerous, and involve intra- and extracellular effects, as well as effects on the cell membrane[x]. Some include the following: absorption of laser photons by water molecules to enhance microcirculation, disassociation of inhibitory nitric oxide from the cytochrome-c oxidase enzyme, activation of light-sensitive ion channels and activation of transcription factors.[xi] The primary effects of PBM occur when there is direct photonic absorption by chromophores in the tissues[xii]. Class 4 therapeutic lasers are FDA-cleared prescription medical devices that can deliver photons of red and infrared laser light to the large volume of tissue required for treatment of peripheral neuropathy.

One study assessed the safety and efficacy of class 4 laser therapy on pain management,

functionality, systemic inflammation, and overall quality of life of patients with diabetic peripheral neuropathy. PBM treatment was delivered to the lumbar region and the plantar surface of the foot, using power levels from 2 to 8 watts. No adverse events were reported during the study period. After the 12-week intervention, pain levels were significantly lower, Timed Up and Go test times (assessing functionality) were significantly improved, and serum levels of IL-6 and MCP-1 were decreased significantly.[xiii]

Another study investigated PBM via class 4 laser therapy for chemotherapy-induced peripheral neuropathy (CIPN). This randomized, double-blinded, sham-controlled, cross-over trial concluded, “Among patients with CIPN, PBM produced significant reduction in neuropathy symptoms.” PBM treatment was delivered to the lumbar region and lower extremity, with power settings from 6.75 to 12 watts, using a combination of continuous wave and pulse frequencies up to 20,000Hz. Treatment times were 30 minutes, and there were no adverse events involving active treatment. The modified total neuropathy score (mTNS), a validated tool that assesses six domains of sensory and motor neuropathy, was used as the outcome measure. The study found that, “photobiomodulation is an effective, low-toxicity treatment for CIPN. Nearly 90% of patients experience significant improvement in mTNS scores that begins within weeks of initiating treatment and persists for at least 10 weeks after the conclusion of therapy. The benefits appear to accrue similarly to patients with variable duration and intensity of neuropathy symptoms, as well as to patients with variable chemotherapy exposures.”[xiv]

In conclusion, peripheral neuropathy is a serious problem regardless of the cause. Standard medical treatments have associated side effects and only mask the symptoms.  Class 4 laser therapy treatments can deliver symptomatic relief, and show great promise in the ability to restore nerve function to the patient suffering from peripheral neuropathy.

[iv] “Updates in diabetic peripheral neuropathy”, Kelsey Juster-Switlyk, A. Gordon Smith; F1000Research 2016, 5:738.
[vii] “The effect of photobiomodulation on chemotherapy-induced peripheral neuropathy: A randomized, sham-controlled clinical trial”, Argenta, et al; Gynecologic Oncology 144 (2017) 159–166.
[viii] “The Mechanistic Basis for Photobiomodulation Therapy of Neuropathic Pain by Near Infrared Laser Light”, Holanda et al; Lasers in Surgery and Medicine. 2017 Jul;49(5):516-524
[ix] “Photobiomodulation induces antinociception, recovers structural aspects and regulates mitochondrial homeostasis in peripheral nerve of diabetic mice”, Oliveira et al; Journal of Biophotonics. 2018;e201800110.
[x] “Basic Mechanisms of Photobiomodulation”, Praveen Arany PhD, presentation at ASLMS meeting, March 29, 2019.
[xi] “Proposed Mechanisms of Photobiomodulation or Low-Level Light Therapy”, Freitas and Hamblin; Journal of Selected Topics on Quantum Electronics. 2016 ; 22(3).
[xii] “Class IV Therapy Lasers Maximize Primary Biostimulative Effects”, Vickers and Harrington; Practical Pain Management, January 2012.
[xiii] “Effect of deep tissue laser therapy treatment on peripheral neuropathic pain in older adults with type 2 diabetes: a pilot randomized clinical trial”, Chatterjee et al; BMC Geriatrics (2019) 19:218.
[xiv] Argenta, et al.