The effects of unilateral transcutaneous electrical nerve stimulation of the median nerve on bilateral somatosensory thresholds

Transcutaneous electrical nerve stimulation (TENS) is used to relieve acute and chronic pain. TENS electrodes are applied at the site of pain or in segments related to the pain, although there is limited research to support either approach. This study investigated the effects of unilateral TENS on mechanical and thermal thresholds at ipsilateral and contralateral sites in healthy human participants. Sensory perception thresholds were measured on the ipsilateral and contralateral thenar eminence of 16 volunteers for von Frey filaments, sharpness, warm, cold and heat pain. TENS was administered over the right median nerve for 10 min at 100 pulses per second (pps) and an intensity which elicited mild tingling in the hand. During TENS, ipsilateral threshold was greater than contralateral threshold for all sensory modalities, although differences were less marked for thermal stimuli. TENS effects had disappeared 30 min after TENS had been switched off although there was a tendency for thermal thresholds to remain elevated. We conclude that during stimulation, TENS elevates somatosensory thresholds within the distribution of the stimulated nerve. The rapid and short-lived ipsilateral effect is consistent with findings from animal studies and suggests a central segmental mechanism.