Quantification of the Effects of Transcutaneous Electrical Nerve Stimulation With Functional Magnetic Resonance Imaging: A Double-Blind Randomized Placebo-Controlled Study

Objective: To evaluate the effects of transcutaneous electric nerve stimulation (TENS) by using functional magnetic resonance imaging (fMRI) in patients with carpal tunnel syndrome (CTS). Design: Randomized controlled trial. Settings: University medical center and an outpatient imaging center. Participants: Female patients with CTS (n=20) were randomized into 2 groups receiving either TENS (n=10) or sham TENS (n=10). In both groups, an initial baseline fMRI session was performed via stimulating digits 2, 5, and 3 in turn, I scan run for each. TENS versus sham TENS treatment was given, and a repeat imaging was performed starting 20 minutes after the treatment as follows: second finger on the 20th minute, fifth finger on the 25th minute (ulnar nerve innervated control finger), and third finger on the 30th min. Interventions: Not applicable. Main Outcome Measure: Differences in fMRI activation between the 2 groups were evaluated. Results: Our results demonstrated that 20 to 25 minutes after TENS treatment-but not in the sham TENS group-a significant fMRI signal decrease for digit 2 (post-TENS vs baseline) was observed in the secondary somatosensory regions, ipsilateral primary motor cortex (M1), contralateral supplementary motor cortex (SMA), contralateral parahippocampal gyrus, contralateral lingual gyrus, and bilateral superior temporal gyrus. Measurements on the 25th to 30th minutes for digit 5 were similar between the groups, with presence of activities in areas other than generally activated regions because of painful stimuli. Thirty to 35 minutes after TENS treatment, a significant fMRI signal decrease for digit 3 was detected in the contralateral M1 and contralateral SMA only in the TENS group. Conclusions: Our findings showed that TENS treatment significantly decreased the pain-related cortical activations caused by stimulation of the median nerve innervated fingers up to 35 minutes after treatment.