The nerve conduction study with the inching method hasbeen 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 invove 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 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 abjoining 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 (0.68±0.07) groups than control (0.382±0.09) and DP (0.81±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 evaluacate the early distal involvement of peripheral heuropathy but also to establish the subclinical
involvement of the segment distal to transverse carpal ligament in CTS with DM group.
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