HIGH-FREQUENCY TRANSCUTANEOUS ELECTRICAL NERVE-STIMULATION ALTERS THERMAL BUT NOT MECHANICAL ALLODYNIA FOLLOWING CHRONIC CONSTRICTION INJURY OF THE RAT SCIATIC-NERVE

Objective: To determine if daily transcutaneous electrical nerve stimu lation (TENS) can alter the thermal and mechanical allodynia that deve lops after chronic constriction injury (CCI) to the right sciatic nerv e of rats Design: A completely randomized experimental design was used . Four groups of rats underwent CCI surgery to the right sciatic nerve and either were not treated with TENS or received TENS starting at di fferent times after the CCI surgery. Interventions: TENS was delivered daily for 1 hour to CCI rats through self-adhesive electrodes applied to skin innervated by the right dorsal rami of lumbar spinal nerves L 1-6. Rats of different groups received daily TENS starting immediately , 20 to 30 hours, or 3 days after the CCI surgery. Main Outcome Measur e: Thermal and mechanical pain thresholds of hind paws were assessed b ilaterally in all rats twice before the CCI surgery (baseline) and the n 2, 7, 12, and 14 days after surgery. Thermal and mechanical allodyni a were expressed as difference scores between the pain thresholds of r ight and left hind paws. These values were normalized to differences t hat existed between the two paws at baseline. Results: Daily TENS begi nning immediately after CCI surgery prevented the development of therm al allodynia at all assessment times (p <.05). Daily TENS starting 1 d ay after surgery reduced thermal allodynia, but only on days 2 and 1 1 (p <.05). Daily TENS beginning 3 days after surgery had no effect on the development of thermal allodynia. Regardless of when it was starte d. daily TENS did not consistently alter mechanical allodynia in CCI r ats Conclusion: It appears that daily TENS can prevent thermal but not mechanical allodynia in this model. However, early intervention with the treatment is critical if it is to be effective at all. (C) 1998 by the American Congress of Rehabilitation Medicine and the American Aca demy of Physical Medicine and Rehabilitation.