Usefulness of the median terminal latency ratio in the diagnosis of carpal tunnel syndrome

ObjectiveThe sensitivity of the median terminal latency (MTL) ratio was compared to that of standard conduction techniques for diagnosing carpal tunnel syndrome (CTS).MethodsWe analyzed 153 patients (274 hands) with clinically suspected CTS and 100 volunteers. Median motor conduction velocity and sensory nerve conduction velocity (MCV and SCV, respectively) were evaluated using traditional methods. The wrist–palm (W–P) MCV and two motor distal latency differences (LDs) between the median and ulnar nerves were measured. The MTL ratio was calculated by dividing the MTL-W by MTL-P. The ratio of distal to proximal conduction (disto-proximal ratio) was calculated.ResultsThe sensitivity of the motor nerve conducting technique was 77.7% in the W–P MCV, 72.6% in the median thenar–ulnar thenar LD, 63.9% in the median thenar–ulnar hypothenar LD, 59.9% in the MTL-P, 60.2% in the MTL-W, and 81.8% in the MTL ratio. The sensitivity of the median sensory nerve conduction method was 89.1% in the W-second F segment, 89.1% in the W-third F segment, 90.5% in the W–P segment, and 92.3% in the disto-proximal ratio of the third finger.ConclusionsThe disto-proximal ratio in the third finger was the most sensitive. Among the motor conduction studies, the MTL ratio was the most sensitive.SignificanceThese ratios can facilitate accurate diagnosis of patients with CTS.