Napadow V, Liu J, Li M, Kwong KK, Kettner N, Hui KKS, Audette J.

An fMRI assessment of cortical plasticity in carpal tunnel syndrome treated with acupuncture.

Department of Radiology, Massachusetts General Hospital, 149 13th St, #2301, Charlestown, MA 02129. vitaly@nmr.mgh.harvard.edu

INTRODUCTION: Carpal tunnel syndrome (CTS) is a common entrapment neuropathy of the distal median nerve, with a U.S. prevalence of 3.72%. Acupuncture may be promising in treating CTS. In this study, fMRI was used with other objective measurements of somatosensory dysfunction to explore the potential efficacy of acupuncture in treating CTS symptomatology including pain and paresthesias.

METHODS: Subjects (n=13) were included if both physical exam (e.g. grip strength, Boston CTS Questionnaire), and nerve conduction findings demonstrated mild to moderate CTS. Outcome measures were assessed at baseline and after two weeks and 5 weeks of acupuncture. fMRI scanning, however, was performed only at baseline and after 5 weeks of acupuncture treatment. Healthy adults (n=12) were also administered physical exam, nerve conduction tests, and were scanned 5 weeks apart. Block design fMRI on a Siemens Allegra 3T system involved innocuous electrical stimulation of digits (D2, D3, D5). Post-processing was completed using FSL and AFNI (SUMA) with Freesurfer reconstructed and inflated brain surfaces in order to assess range and somatotopy of cortical activity.

RESULTS: fMRI activation with stimulation of median nerve innervated D2 and D3 demonstrated more widespread activity in contralateral Brodmann Area 1 (BA1, a subarea of SI) for CTS patients compared with healthy subjects (p<0.05). Stimulation of ulnar nerve innervated D5 produced less profound differences between CTS patients and healthy adults. Analysis of somatotopy suggested that the cortical separation distance of the contralateral SI representations of D2 and D3 was less for CTS patients (3.8±1.0mm) than for healthy adults (7.5±1.2mm). Furthermore, the D3/D2 separation distance correlated negatively with D2 sensory conduction latency Ð the greater the latency, the closer the D2/D3 cortical representations. After acupuncture treatment, dysesthesias were significantly diminished (p<0.005), median nerve latencies for affected digits decreased (p<0.05), and grip strength was improved (p<0.05). Contralateral BA1 activity was diminished for D3 compared to pre-treatment (p<0.005), while a lateral shift in the D2 representation served to increase the D2/D3 separation distance (p<0.05) for CTS patients. We propose that multidigit paresthesias and pain in CTS patients constitute aberrant afferentation, which serves to amplify (disinhibit) and blur affected digit cortical representation through Hebbian plasticity mechanisms. Further, acupuncture (a somatosensory conditioning stimulus) may be an effective modality to improve the symptomatology of CTS and induce beneficial cortical plasticity.

 

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