Outcome prediction value of nerve conduction studies for endoscopic carpal tunnel surgery.

OBJECTIVE: Carpal tunnel syndrome is the most common entrapment neuropathy. We explore the clinical use of nerve conduction study in the outcome prediction and preoperative selection for endoscopic carpal tunnel syndrome surgery.
METHODS: Sixty-seven patients with carpal tunnel syndrome were prospectively enrolled. Each patient's clinical symptomatic score at baseline and 3 months postsurgery was compared with nerve conduction study parameters of distal motor latency, motor amplitude, motor conduction velocity, distal sensory latency, sensory amplitude, and sensory conduction velocity. A statistical logistic regression model was used to ascertain outcomes.
RESULTS: Endoscopic surgery resulted in significant improvement for all four major symptoms pain, numbness, paresthesia, and weakness. From multivariate logistic regression, a shorter distal sensory latency is associated with a higher likelihood of a good outcome (P = 0.058; odds ratio, 0.912; 95% confidence interval, 0.828-1.0) only for paresthesia. The other factors were not found to be significant (all P > 0.10). The area under the curve (AUC) was 0.69 (95% confidence interval for AUC, 0.50-0.88). A cutoff of 6.0 ms or lower for sensory latency predicts for good outcome (in terms of paresthesia score) with the sensitivity/certainty of 84.6% and positive predictive value of 86.8%. A receiver operating characteristic analysis of baseline paresthesia score for good outcome of the paraesthesia domain showed that the AUC was 0.967 (95% confidence interval for AUC, 0-1.0). At a cutoff of baseline paraesthesia score of 4 or above, prediction for good outcome achieved a sensitivity of 87.2% and positive predictive value of 97.1%.
CONCLUSIONS: A shorter distal sensory latency is associated with a higher likelihood of a good outcome for paraesthesia. In addition, patients with baseline of 4 or above had correlated with better surgical outcome than those with less severe symptoms. Our data thus suggest that surgical benefit is best seen in patients with moderate symptoms, in combination with electrophysiological evidence of early demyelination, as a possible therapeutic window.