Transcutaneous Electrical Nerve Stimulation
Transcutaneous electrical nerve stimulation (TENS) currently is one of the most commonly used forms of electroanalgesia. Hundreds of clinical reports exist concerning the use of TENS for various types of conditions, such as low back pain (LBP), myofascial and arthritic pain, sympathetically mediated pain, bladder incontinence, neurogenic pain, visceral pain, and postsurgical pain.
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)5
- Direct inhibition of an abnormally excited nerve
- Restoration of afferent input
The results of laboratory studies suggest that electrical stimulation delivered by a TENS unit reduces pain through nociceptive inhibition at the presynaptic level in the dorsal horn, thus limiting its central transmission. The electrical stimuli on the skin preferentially activate low-threshold, myelinated nerve fibers. The afferent input from these fibers inhibits propagation of nociception carried in the small, unmyelinated C fibers by blocking transmission along these fibers to the target or T cells located in the substantia gelatinosa of the dorsal horn.
Indications for the use of TENS
- Neurogenic Pain (eg, deafferentation pain, phantom pain), sympathetically mediated pain, postherpetic neuralgia, trigeminal neuralgia, atypical facial pain, brachial plexus avulsion, pain after spinal cord injury (SCI)
- Musculoskeletal Pain - Examples of specific diagnoses include joint pain from rheumatoid arthritis and osteoarthritis, acute postoperative pain (eg, postthoracotomy), and acute posttraumatic pain.10,11,12,13,14,15,16 After surgery, TENS is most effective for mild to moderate levels of pain, and it is ineffective for severe pain. The use of TENS in chronic LBP and myofascial pain is controversial, with placebo-controlled studies failing to show statistically significant beneficial results. Uncertainty also exists about the value of TENS in tension headache.
- Visceral Pain and Dysmenorrhea - TENS has been successfully applied to these conditions as well.
- Other Disorders - TENS has been used successfully in patients with angina pectoris and urge incontinence, as well as in patients requiring dental anesthesia. Reports discuss the use of TENS to assist patients in regaining motor function following stroke, to control nausea in patients undergoing chemotherapy, as an opioid -sparing modality in postoperative recovery, and in postfracture pain.