CONDUCTION BLOCK AND SEGMENTAL VELOCITIES IN CARPAL-TUNNEL SYNDROME

In carpal tunnel syndrome (CTS) standard measurement of median distal motor latency and sensory conduction does not distinguish whether low amplitude responses are due to axonal degeneration or demyelination. I n 88 control and 294 CTS hands we recorded amplitude and duration of c ompound muscle action potential (CMAP) and of antidromic sensory nerve action potential (SNAP) after palm and wrist stimulation to determine wrist to palm amplitude, duration ratios and se,omental conduction ve locities. In 16% of CTS hands there was an abnormal amplitude reductio n without increased duration of CMAP or SNAP from wrist stimulation in dicating partial conduction block. In 148 hands distal motor latency t o abductor pollicis brevis and/or sensory conduction to digit 2 were a bnormal. In the remaining 146 hands wrist to palm motor conduction was less than 35 m/s in 22.6% and wrist to palm sensory conduction was le ss than 45 m/s in 13%. At least one segmental conduction was abnormal in 27% of hands. Segmental studies allow the discrimination between co nduction block and axonal degeneration, increase diagnostic yield in C TS, and might be useful in addressing treatment and predicting outcome . (C) 1997 Elsevier Science Ireland Ltd.