Introduction:
Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy in society. Based on the data obtained from basic conventional CTS studies, patients can be staged, and the changes in CTS severity can be followed according to the electrophysiological parameters derived from the data. This study aimed to assess the electrophysiological findings of CTS patients using the Bland and Padua grading systems and median terminal latency index (mTLI) and to evaluate the findings that may indicate the transition to the advanced stage.

Material and methods:
The study included 822 patients. After electrophysiological examination, both hands of the patients were staged according to the grading systems proposed by Padua and Bland. Additionally, mTLI was calculated for each hand.

Results:
With the increase in stages, a significant decrease was found in mTLI, median sensory nerve conduction velocity (mSNCV), median sensory amplitude (mSA), median motor nerve conduction velocity (mMNCV), and median motor amplitude (mMA), whereas a significant increase was observed in median sensory distal latency (mSDL) and median motor distal latency (mMDL) (p < 0.001) The parameter with the highest sensitivity regarding the indication of transition between stages was mSNCV; the sensitivity increased with the progression of stage, and a cut-off value of 40.5 m/s showed a sensitivity of 94.2% and a specificity of 90% regarding the indication of transition to the advanced stage.

Conclusions:
Our results showed that with a cut-off value of 40.5 m/s, mSNCV is an accurate, sensitive and specific parameter regarding the indication of transition to the advanced stage.