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)
- Direct inhibition of an abnormally excited nerve
- Restoration of
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 (laminae 2 and 3) of the dorsal horn.
When TENS is used analgesically,
patients are instructed to try different frequencies and intensities to find those that provide them with the best pain control.
Optimal settings of stimulus parameters are subjective and are determined by trial and error. Electrode positioning is quite
important. Usually, the electrodes are initially placed on the skin over the painful area, but other locations (eg, over cutaneous
nerves, trigger points, acupuncture sites) may give comparable or even better pain relief.