Physiological Localization by Sensory and Motor Inching Studies and Structural Abnormalities Detected by Ultrasonographic Changes in Carpal Tunnel Syndrome.

Abstract Objective To study mild to moderate carpal tunnel syndrome (CTS), compare median nerve entrapment sites detected by electrophysiologic inching studies with ultrasonographic abnormalities of cross-sectional area (CSA), and correlate focal points of conduction delays detected by sensory and motor inching recorded from the third digit and second lumbrical muscle Design Analytic cross-sectional study Setting Department of Rehabilitation Medicine, King Chulalongkorn Memorial Hospital. Participants A total of 15 normal hands from 10 healthy participants and 40 hands with mild to moderate CTS from 29 participants were selected by convenience sampling. Interventions Not applicable Main Outcome Measure Correlation of electrophysiologic entrapment site localization by inching study with anatomical entrapment site detected by ultrasound (US). Results In all 40 hands tested, a sharply localized latency was found to increase across a 1 cm segment, most commonly 2–3 cm distal to the distal wrist crease for both sensory and motor studies, showing a good match between the two with Pearson correlation coefficient value, r = 0.72. The US revealed a narrowing CSA of the median nerve at 1–2 cm distal to the distal wrist crease. Conclusions This study showed a high correlation for focal point conduction delay detected by sensory and motor nerve conduction study. Recording from the second lumbricalis facilitated motor inching along the straight course of the nerve instead of the arcuate recurrent branch innervating the abductor pollicis brevis, the muscle traditionally used. US examination also revealed a localized narrowing of the median nerve CSA at 1–2 cm distal to the distal wrist crease, a possible site for anatomical entrapment. The most enlarged CSA was seen at the distal wrist crease, a level corresponding to the inlet of the carpal tunnel. Thai Clinical Trials Registry Number TCTR20190605001