[Carpal tunnel syndrome: sensory median-radial latency difference versus conduction studies in 1059 hands (668...

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) > or = 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 > or = 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 > or = 3.01 ms, middle finger > or = 3.14 ms and ring finger > or = 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 > or = 1.0 ms is very sensitive for CTS diagnosis.