Median neuropathy at the wrist: Diagnostic utility of clinical findings and an automated electrodiagnostic device

Clinical findings have limited value in predicting electrophysiologically c onfirmed median neuropathy at the wrist (MNW). To determine the value of cl inical findings and an automated electrophysiologic neurodiagnostic device (AEND) in diagnosing MNW, we studied two groups of 75 consecutive patients (an initial group and a validation group, 150 total) referred to an academi c electrophysiology laboratory for upper extremity complaints The definitiv e standard for MNW was the neurologist's diagnosis after formal clinical an d electrodiagnostic evaluation. The neurologist was blinded to the results of the AEND (NC-Stat(TM), NeuroMetrix, Inc). In the validation group, the A END yielded a distal motor latency (DML) in 97% of hands with a conventiona l motor response, and the correlation of the AEND DML with the conventional DML was 0.94 (P < 0.001). Of 248 symptomatic hands, the neurologist diagno sed 117 (47%) with MNW: At 90% specificity, the AEND DML, had a sensitivity of 86% fm MNW: Age, body mass index, sensory symptoms in digits I to 3, an d nocturnal awakening were independent clinical predictors of MNW. Each I-m sec increase in the adjusted AEND DML was independently associated with an OR of 298 (95% confidence interval, 40 to 2233) for MNW: Each I-msec increa se in the F-wave latency was independently associated with an OR of 2.6 (95 % confidence interval 1.3 to 4.9) for MNW. Compared with a model based sole ly on clinical variables, an algorithm including symptom variables plus the AEND DML had an odds ratio for correct diagnostic classification of 6.3 (9 5% confidence interval, 3.8 to 12.3). The sensitivity at 90% specificity im proved fi om 40% for the clinical model to 86% for the model with DML. A pr actical method for integrating clinical and electrophysiologic findings to assess the risk of MNW was proposed. This method correctly stratified 79% o f control and MNW patients into very low and high-risk groups, respectively . We concluded that MNW diagnosis is significantly improved with an AEND.