A comparison of traditional electrodiagnostic studies, electroneurometry, and vibrometry in the diagnosis of carpal tunnel syndrome

In 49 patients (98 hands), referred to an electrodiagnostic laboratory, assessments were made by conventional nerve conduction studies on the upper extremity and by two more portable modalities, namely electroneurometry (skin surface electrical stimulation of the motor nerve) and single-frequency (120 Hz) vibrometry. Tests were performed on median and ulnar nerves. Correlations with motor nerve conduction studies for each screening test on the median nerve were r=.81 For the electroneurometer and r=.48 for the vibrometer. When carpal tunnel syndrome was diagnosed either by clinical criteria only or by nerve conduction abnormality, the association with electroneurometry was characterized by high sensitivity and low specificity, while the opposite relationship prevailed with vibrometry. These associations were highly dependent on the methods used to select normal values from a reference population. While the manufacturer's recommended normal values offered good predictability, with thresholds that corresponded to nerve conduction studies, normal values generated in a more standard way produced much weaker and less useful associations. The selection of an appropriate electrical screening test for peripheral nerve injury, such as entrapment neuropathy, depends on the prevalence and seriousness of the target disease and the relative consequences of over- and underdiagnosis.