Evaluation of electrical activity at the carpal tunnel area in response to median nerve elbow stimulation using magnetoneurography.

OBJECTIVE

To develop a magnetic field measurement method in the carpal tunnel area in response to electrical median nerve stimulation at the elbow and evaluate its usefulness.

METHODS

Five healthy subjects participated. The magnetic field recording evoked by median nerve electrical stimulation at the elbow with electrical intensity that minimized the pronator quadratus and flexor carpi radialis muscle response was measured with 132-channel superconducting quantum interference device magnetoneurography. The current distributions were reconstructed from magnetic fields with the spatial filter method. The magnetic fields evoked by electrical stimulation at the index distal interphalangeal joint were also measured.

RESULTS

After median nerve elbow stimulation, intra-axonal current and inward currents flowing perpendicularly to the nerve pathway were visualized. The mean ± SD inward current intensity at the center of the carpal tunnel area was significantly larger with elbow stimulation than with index distal interphalangeal joint stimulation: 1.11 ± 0.65 nAm versus 0.51 ± 0.15 nAm (p = 0.047).

CONCLUSIONS

Magnetic field measurement in the carpal tunnel area with adjusted submaximal stimulation at the elbow can detect larger signals compared with digit stimulation.

SIGNIFICANCE: This method has the potential to be more useful for the examination of carpal tunnel syndrome patients.