Comparison of median nerve conduction parameters from the index and middle fingers in carpal tunnel syndrome: Toward a standardized electrophysiological evaluation protocol.

BACKGROUND

Variability exists regarding which is the best digit for diagnosing and classifying the severity of carpal tunnel syndrome (CTS) with electrodiagnostic studies.

OBJECTIVE

To compare nerve conduction parameters-peak sensory latency, amplitude, and conduction velocity-of the median nerve between the index and middle fingers in patients with mild to moderate CTS and to assess the diagnostic value of interdigit latency differences.

DESIGN

Diagnostic study with the gold standard of electrodiagnosis.

SETTING

Department of physical medicine and rehabilitation at a tertiary hospital affiliated with a university of medical sciences.

PARTICIPANTS

Participants were adult patients with a clinical diagnosis of primary idiopathic mild (n = 53) or moderate (n = 53) CTS, along with a control group (n = 53) with no electrodiagnostic evidence of CTS.

INTERVENTIONS: Not applicable.

MAIN OUTCOME MEASURE: Antidromic sensory nerve conduction studies were performed on the index and middle fingers, and the parameters were compared among the study groups. Linear regression and supervised machine learning models, adjusted for age and body mass index, were used to evaluate diagnostic performance.

RESULTS

Peak sensory latencies increased with the severity of CTS for both the index and middle fingers (both p <.001). The difference in interdigit latency also increased significantly with syndrome severity (p < .001). Post hoc tests revealed significant differences in interdigit latencies for all pairwise comparisons among the study groups (all p < .001). Multivariable models adjusted for age and body mass index achieved the highest diagnostic accuracy for middle finger latency (area under the receiver operating characteristic curve = 0.973, p < .001). The interdigit latency difference model demonstrated the highest sensitivity (90%) for moderate CTS.

CONCLUSIONS

Middle finger peak latency outperformed index finger recordings and interdigit latency comparisons in diagnosing CTS. Adding middle finger peak latency and interdigit latency difference to standard electrodiagnostic protocols improves early detection and classification of the syndrome.