Does neuromodulator electrical stimulation work for peripheral pain relief? What is the mechanism of action?
—Jorge Guzman Ortiz, MD, Jayuya, P.R.

Transcutaneous electrical nerve stimulation (TENS) therapy has been commonly employed in the treatment of peripheral pain, but its mechanism of action is unknown and its efficacy is questionable. One proposed mechanism of action is that electrical stimulation reduces pain through nociceptive inhibition at the presynaptic level in the dorsal horn, thereby limiting its central transmission. Another hypothesis suggests endogenous pain control via release of endorphins, enkephalins, and dynorphins. Unfortunately, a recent Cochrane review analyzing 19 randomized controlled trials failed to find sufficient data to perform a meta-analysis and reported that there was inadequate evidence to draw any conclusions about efficacy of TENS (Cochrane Database Syst Rev. 2001;[3]:CD003222). In contrast, percutaneous electrical nerve stimulation (PENS) may be more effective than TENS or exercise therapy, at least in patients with chronic low back pain (J Am Geriatr Soc. 2003;51:599-608). This technique uses acupuncturelike needle probes to stimulate peripheral sensory nerves while bypassing local skin resistance.
—Daniel G. Tobin, MD (108-7)