Influence of pain reduction by transcutaneous electrical nerve stimulation (TENS) on somatosensory functions in patients with painful traumatic peripheral partial nerve injury.

Following peripheral nerve injury sensory loss is taken as a sign of denervation. However, based on reports of improved sensitivity following relief of pain it has been suggested that a functional block produced by the activity in the nociceptive system itself may be responsible for at least part of the sensory aberrations. The aim was to examine if pain reduction by high-frequency TENS influenced somatosensory functions in patients with long-term unilateral painful traumatic peripheral partial nerve injury. Eighteen patients with spontaneous ongoing pain and a touch sensation in the innervation territory of the injured nervous structure of at least 5 on an intensity 11-point Likert rating scale compared with contralaterally, participated. Before and following 80 Hz TENS with a stimulus intensity generating non-painful paresthesiae in the painful areas during 30 min the pain intensity was rated on a numerical rating scale and bedside examination of somatosensory functions (BE) and quantitative sensory testing (QST) were performed in the same areas. Before and following TENS there was no difference in sensory functions between nine patients with ≥ 50% pain reduction and nine patients with a smaller or no reduction in pain. Compared to baseline, only minor TENS-induced alterations in somatosensory functions were found at BE in conjunction with decreased sensitivity to light touch at QST (p < 0.01) in both groups alike. In conclusion ≥ 50% pain reduction by TENS did not alter sensory functions differentially compared to a smaller or no reduction in pain.