SEGMENTAL INCHING OF MEDIAN NERVE: ESTABLISHING ABNORMAL CUT-OFF VALUE TO DIAGNOSE CARPEL TUNNEL SYNDROME


Dilip Thakur, Bishnu Hari Paudel, Shiva Raj Paneru

Abstract
This study was aimed to obtain preliminary normative data of median sensory nerve inching in our setup and population for electrodiagnosis of carpal tunnel syndrome (CTS). Orthodromic inching of the median nerve was performed by stimulating the second digit of 42 wrists (14 males and 7 females. The mean ages of males and females were 28.1±1.68 yrs and 26.4±3.6 yrs respectively. The sensory nerve action potential (SNAP) latency and amplitude were measured in segments 3 cm proximal to the distal wrist crease and 4 cm distal to it. The mean SNAP latency and amplitude in males was 1.93±0.31ms and 30.53±10.65µV respectively. In females, the mean SNAP latency was 1.75±0.2ms and amplitude, 32.8±10.41 µV. The mean conduction delay per centimeter (CD/cm) was 0.19ms in both genders. The maximal CD/cm was 0.3ms in males and 0.35ms in females in the segment 1cm distal to the distal wrist crease. The abnormal cut-off value, calculated as the maximal CD/cm + 2SD was 0.63/0.57ms in males and females respectively. Since, these nerve conduction study parameters vary with the laboratory conditions, demographic profile and anthropometric measurements of the population; this median sensory nerve inching study provides preliminary normative data that will aid in electrodiagnosis of CTS.

Keywords: carpal tunnel, conduction delay, inching, sensory