Electrophysiological Studies with Inching Method in Carpal Tunnel Syndrome

ABSTRACT

The nerve conduction study with the inching method has been performed to characterize the nature of lesion (focal of diffuse) within the carpal tunnel and to increase the diagnostic sensibility of the carpal tunnel syndrome (CTS). The sensory nerve conduction velocity of finger-to-palm (F-P) segment of median never or the ratio of sensory nerve conduction velocity of palm-to-wrist (PW) segment to F-P segment of the median nerve (P-W/F-P ratio) was also measured to differentiate the CTS from the early peripheral polyneuropathy, which may only involve the median nerve. Conduction times of the sensory median nerve between the midpalm and the distal forearm in 2cm increments were measured orthodromically in controls (n=32) and CTS patients. The P-W/F-P ratio in control, CTS without diabetes mellitus (DM) (n=23), CTS with DM (n=9), and diabetic peripheral polyneuropathy (DP) groups was compared. The criteria for focal lesion within the carpal tunnel were defined as follows 1) If the maximal conduction time is located at 4-2cm segment distal(designated as '-') to distal wrist crease, it must be prolonged more than 4 times that of the adjoining distal segment or 6 times that of adjoining proximal segment. 2) If the maximal conduction time is located at -6--4cm segment, it must be beprolonged more than 4 times that of the adjoining proximal segment. According to above criteria, the incidened of focal lesion within the carpal tunnel was 84.4%(27/32) and the most common segment of focal lesion was -4--2cm segment(85.2%, 23/27). The P-W/F-P ratio was more decreased in CTS without DM (0. 55 + 0. 11) and CTS with DM(O.68+0.07) groups than control(0382+0.09) and DP(O.81+0.09) groups(P<0.01). In CTS groups, it was more decreased in CTS without DM group than CTS with DM group(p<0.05). So the measurement of sensory nerve conduction velocity of F-P segment of median nerve or the P-W/F-P ratio is helpful not only to evalucate the early distal involvement of peripheral neuropathy but also to establish the subclinical involvement of the segment distal to transverse carpal ligament in CTS with DM group.