Nerve stimulation and neuromodulation for painful nerves: a narrative review.

Abstract

Nerve injury primarily leads to neuropathic pain but may also have overlapping elements of nociplastic pain or ongoing nociceptive pain. Electrical stimulation is particularly effective in the treatment of neuropathic pain and may be effective for nociplastic and nociceptive pain. While multiple mechanisms contribute to the analgesic effect of electrical stimulation, the most widely accepted theory for the predominant effect is that of Melzack and Wall's gate control theory. According to this theory, non-painful sensory input carried by low-threshold large-diameter Aβ fibres disrupt the transmission of pain signals in small pain fibers (Aδ and C fibres). This occurs through the activation of inhibitory interneurons in the dorsal horn, which ultimately blocks pain signal transmission.This theory has been employed for different forms of stimulation, including transcutaneous electrical nerve stimulation (TENS), percutaneous electrical nerve stimulation (PENS), and peripheral nerve stimulation (PNS). Each of these methods offers a different approach to localized stimulation and neuromodulation for the treatment of pain. TENS is a non-invasive technique, that delivers electrical currents via surface electrodes placed on the skin. PENS, in contrast, is a minimally invasive method that applies electrical currents through small needles inserted near a target muscle or neural structure. PNS involves the implantation of temporary or permanent electrodes to deliver electrical stimulation directly to peripheral nerves. These modalities are widely used to manage various pain conditions including non-malignant, chronic musculoskeletal and neuropathic pain, such as chronic low back pain, neck pain, neuropathic pain, myofascial pain, and post-operative pain. TENS is particularly notable as a non-invasive device that is affordable, over-the-counter, self-administered, and nonpharmacological option that does not pose the risk of toxicity or overdose. PENS stands out for its ability to integrate electrical stimulation therapy with electroacupuncture through a minimally invasive technique. PNS, on the other hand, is unique in its capacity to precisely target specific nerves and provide a range of stimulation options for extended treatment durations.This article provides a narrative overview of TENS, PENS and PNS with a particular focus on their application for neuropathic pain management and for athletes. We will review mechanisms of action, indications, diagnostic and treatment algorithms, as well as complications and limitations. The overview concludes with a complex case study demonstrating the use of various electrical stimulation therapies, ultimately to successful pain resolution for the patient.