Transcutaneous Electrical Nerve Stimulation (TENS) is a form of electrotherapy which makes use a of a convenient device that applies an electrical current through the skin to stimulate sensory nerves and trigger the release of endorphins, hormones with a pain relieving property that provide a natural and effective relief of chronic pain. TENS is actually quite a broad category describing a range of different techniques based on applying electrical stimulation through the skin, but within physiotherapy its use is generally focused on the relief of symptomatic pain, particularly in instances of chronic pain that isn’t being dealt with effectively by means of medication.
The main advantage of TENS is that it makes use of natural pain relieving mechanisms, and hence has minimal side effects. Drug therapies effectively introduce foreign chemicals to achieve the same end, but in doing so alter your metabolism and bodily function, hence causing more potential side effects. The main use in physiotherapy for TENS is as a means of relieving chronic pain relief without the risk of drug interactions and/or side effects.
TENS devices can provide a range of frequencies which allow them to tailor to a broad range of physiologies, each of which may respond differently under a range of stimulation. New machines are becoming more compact and easy to use, allowing for patients to use the therapy in the comfort and privacy of home after instruction and guidance from a physio.
TENS will often be used in conjunction with other forms of physical therapy for the best clinical outcomes. Using the technique in conjunction with hot and cold therapies, hydrotherapy, stretching, and therapeutic exercise is common practice.
The mechanism of the analgesia produced by TENS is explained by the gate-control theory proposed by Melzack and Wall in 1965. The gate usually is closed, inhibiting constant nociceptive transmission via C fibers from the periphery to the T cell. When painful peripheral stimulation occurs, however, the information carried by C fibers reaches the T cells and opens the gate, allowing pain transmission centrally to the thalamus and cortex, where it is interpreted as pain. The gate-control theory postulates a mechanism by which the gate is closed again, preventing further central transmission of the nociceptive information to the cortex. The proposed mechanism for closing the gate is inhibition of the C-fiber nociception by impulses in activated myelinated fibers.
The currently proposed mechanisms by which TENS produces neuromodulation include the following:
Presynaptic inhibition in the dorsal horn of the spinal cord
Endogenous pain control (via endorphins, enkephalins, and dynorphins)