Objective
To investigate the reliability of distoproximal latency ratio of median sensory nerve as a diagnostic criterion of carpal tunnel syndrome (CTS) in patients with diabetic polyneuropathy.

Subject: Electrophysiologic study was performed in 264 hands of 208 patients with diabetes. Forty eight hands (24 subjects) without diabetes mellitus or CTS were included as a normal control group. Another 48 hands having CTS without diabetes mellitus were also included as a CTS control group.

Method
Clinical and electrophysiologic findings were included to detect carpal tunnel syndrome in patients with diabetic neuropathy. Sensitivity and specificity of various electrodiagnostic parameters to confirm clinical CTS were obtained.

Results
Diabetic neuropathy was diagnosed in 66.3%, and median neuropathy was diagnosed in 52.7%. CTS was found in 32.2% as determined by the distoproximal latency ratio. The sensitivity of distoproximal latency ratio as a diagnostic tool for CTS was the highest (95.1%) and the specificity was the second highest (51.3%) among 5 different electrodiagnostic criteria of CTS.

Conclusion
The results suggest that distoproximal latency ratio is an important parameter with high sensitivity in determining CTS in the patients with diabetic polyneuropathy.