A neurophysiological grading scale for carpal tunnel syndrome.

Different ways of expressing the severity of carpal tunnel syndrome (CTS) are found in the existing literature and in clinical records. This paper documents the distribution of patients on a scale based upon the nerve conduction study findings, which are largely independent of the exact normal values used in any given laboratory and demonstrate a highly significant linear relationship between the neurophysiological grading and a numerical score derived from the clinical history. Patients with more characteristic stories of CTS generally have higher neurophysiological grades. The scale is as follows: normal (grade 0); very mild (grade 1), CTS demonstrable only with most sensitive tests; mild (grade 2), sensory nerve conduction velocity slow on finger/wrist measurement, normal terminal motor latency; moderate (grade 3), sensory potential preserved with motor slowing, distal motor latency to abductor pollicis brevis (APB) < 6.5 ms; severe (grade 4), sensory potentials absent but motor response preserved, distal motor latency to APB < 6. 5 ms; very severe (grade 5), terminal latency to APB > 6.5 ms; extremely severe (grade 6), sensory and motor potentials effectively unrecordable (surface motor potential from APB < 0.2 mV amplitude).