Neurophysiological assessment of the early phases of carpal tunnel syndrome with the inching technique before and during operation.

In 14 patients with early carpal tunnel syndrome, the diagnostic sensitivity of the measurement of the segmental sensory nerve conduction velocity at 1 cm. steps ("inching") was compared with the distal sensory latency and the pre-operative wrist-digit and wrist-palm S.C.V. and with similar measurements made at operation immediately after surgical decompression of the nerve. Before operation, distal sensory latency and wrist-digit S.C.V. were normal in all cases, while wrist-palm S.C.V. was pathological in five patients and inching in all 14 patients. Moreover, inching allowed us to determine the site of the slowing across the carpal tunnel, this being between 1-2 cm. from the distal wrist crease in 57% and between 2-3 cm. in 21% of cases. Focal slowing disappeared immediately after decompression in five patients, as is evident from the intra-operative recordings. Inching is, therefore, the most sensitive diagnostic method in early carpal tunnel syndrome.