Residual Latency and Terminal Latency Index in Diabetic Patients with Asymptomatic Electrophysiologic Carpal Tunnel Syndrome

Objectives: Carpal tunnel syndrome (CTS) in diabetic patients is frequently asymptomatic and its relationship to polyneuropathy is not clear. This study aimed to determine whether the presence of asymptomatic electrophysiologic CTS is associated with an increased risk of polyneuropathy in diabetic patients using residual latency (RL) and terminal latency index (TLI). Methods: We included 12 diabetic patients with asymptomatic electrophysiologic CTS. Control values were obtained from 21 healthy subjects. For comparison, we had recruited 41 diabetic patients with polyneuropathy (PN) and 50 patients with CTS without diabetes. The RL is a subtraction of the calculated latency from the measured latency and was determined following the formula RL = terminal latency (ms) - [terminal distance (mm) ÷ proximal conduction velocity (m/s)]. The TLI was used to compare the wrist-to-thenar muscle with the elbow-to-wrist segment conduction velocity. We used the formula TLI = terminal distance (mm)/ [proximal velocity (m/s) x terminal latency (ms)]. Statistical analysis was performed by SPSS version 10.0. Results: There was no significant difference for RL among normal controls, patients with asymptomatic electrophysiologic CTS, and CTS patients without diabetes except median nerve. Diabetic patients with polyneuropathy showed significant increase in RL and TLI compared to normal controls. Conclusion: The ulnar, peroneal, and tibial nerve RL values were not different in diabetic patients with asymptomatic electrophysiologic CTS compared to normal controls. These findings suggest asymptomatic electrophysiologic CTS in diabetic patients is related with focal entrapment rather than an early polyneuropathy. We found the RL was more concordant with nerve conduction than TLI.ope