Between January 1989 and June 1996, 1 059 carpal tunnel syndrome hands (CTS) from 668 patients were studied. None had been previously operated and all had bilateral conduction studies; peripheral neuropathy was excluded. The patients were selected with sensory median/radial difference (MRD) >1.0 ms that strongly supports electrodiagnosis of CTS (standard deviation > 6) after simultaneous stimulation on wrist and recording on thumb. Normal MRD were obtained in 125 hands with upper limit of normality = 0,43 ms (mean + 2SD). The age ranged from 17 to 83 years (mean 47.5) and 91.3% were female. MRD >1.0 ms correlates in 95% with median distal motor latency >4.25 ms (80 mm distance) and with median distal sensory latency to index finger >3.01 ms, middle finger >3.14 ms and ring finger >3.26 ms, all of them 140 mm distance, antidromic and onset-measured. The results have brought new values for the limit of normality in our EMG laboratory since MRD >1.0 ms is very sensitive for CTS diagnosis.
carpal tunnel syndrome; median nerve; compression neuropathy; mononeuropathy; nerve conduction study
