Effect of Acupuncture in Carpal Tunnel Syndrome on Somatosensory Cortical Plasticity

Carpal tunnel syndrome (CTS) is a common entrapment neuropathy, with a U.S. prevalence of 3.72%, and includes compression of the distal median nerve. Acupuncture may be promising in treating CTS.

For this project, 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. Patients (n=13) were included if both physical exam (e.g. grip strength, Boston CTS Questionnaire), and nerve conduction findings demonstrated mild to moderate CTS. CTS patients were evaluated prior to, two weeks into, and after 5 weeks of acupuncture, and were scanned with fMRI before and after acupuncture treatment. Healthy adults (n=12) were also administered physical exam and 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. FMRI activation for stimulation of CTS affected D2, and D3 demonstrated more widespread activity in contralateral BA1 for CTS patients compared with healthy subjects (p<0.05). Moreover, D3 fMRI activation in both the contralateral SI and motor cortex correlated positively with the D3 sensory conduction latency. Analysis of somatotopy suggested that contralateral SI representations for D2 and D3 were less separated 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 - the greater the latency, the closer the D2/D3 cortical representations.

After acupuncture treatment, neuropathic pain was significantly diminished (p<0.005), 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 the serves to blur affected digit cortical representation through Hebbian plasticity mechanisms. Further, acupuncture, a somatosensory conditioning stimulus, may be an effective modality in improving the symptomatology of CTS and inducing beneficial cortical plasticity.