Transcutaneous Electrical Nerve Stimulation (TENS) is commonly used as an electroanalgesic and has been shown to be efficacious in the treatment of chronic musculoskeletal pain (Johnson et al. 2007). TENS is believed to preferentially stimulate large alpha sensory nerves and reduce pain at the presynaptic level in the dorsal horn of the spinal cord through nociceptive inhibition (Cheing et al. 1999).
Norrbrink (2009) in a crossover study examined the effect of low frequency (2Hz) or high frequency (80Hz) TENS stimulation. Patients received either low or high frequency stimulation for 30 to 40 minutes 3 times a day for 2 weeks followed by a 2 week washout period. They then switched stimulation frequency groups. The authors reported no significant difference between the two treatments in improving neuropathic pain. However, the study did find clinically significant reductions of pain intensity, worst pain intensity and pain unpleasantness post treatment when compared to baseline scores. In 70% of participants there was a decrease of greater than 2 points in pain intensity from baseline; where clinical significance was defined as having a reduction of greater than 1.8 points.
Davis and Lentini (1975) reported on a series of patients (n=31) in whom transcutaneous nerve stimulation was applied to painful areas. Among those with a thoracic (n=11) or caudal level injury (n=16), only 36% reported that the treatment was successful in reducing pain at the injury site; meanwhile, none of those with a cervical injury (n=4) experienced any reduction in pain. In general, TENS was not deemed effective for radicular or below-level injury site pain.
There is level 4 evidence (from one case series study; Davis & Lentini 1975) that transcutaneous electrical nerve stimulation reduced at-the-injury site pain in only a minority of patients with thoracic or cauda equina SCI, but not those with cervical SCI.
Transcutaneous electrical nerve stimulation may reduce pain at site of injury in patients with thoracic but not cervical injury.