Efficiency of 90-Min Extended EMLA-Induced Stimulated Skin-Wrinkling Test in the Diagnosis of Carpal Tunnel Syndrome

BACKGROUND: Previous researchers have used a 30-min eutectic mixture of local anesthetic (EMLA) test, which assesses the sympathetically mediated vasomotor function, in diagnosing carpal tunnel syndrome (CTS). However, its specificity was low, limiting its clinical diagnostic utility. In this study, we assessed the efficiency of 90-min extended EMLA-induced stimulated skin-wrinkling (SSW) test in CTS diagnosis. METHODS: A cross-sectional study was designed among patients clinically diagnosed with CTS. Hands of healthy volunteers and the asymptomatic hands of selected patients served as control. The Boston symptom severity scale (SSS) and the neuropathic pain severity inventory (NPSI) were used to assess symptom severity, and nerve conduction study (NCS) was used to assess electrophysiological severity. EMLA-induced SSW was visually graded after 90 min of application and correlated with symptom and NCS severities. RESULTS: Forty-two symptomatic hands and 30 asymptomatic hands were enrolled as cases and controls, respectively. The diagnostic efficiency of the extended EMLA test was found to be 83.4% for digit 2 and 87.3% for the lateral 4 digits (mean), whereas the diagnostic efficiency of standard NCS was 88.1%. Boston SSS and NPSI were better correlated with EMLA positivity than NCS positivity. A linear regression analysis showed negative correlation of wrinkling grade with NCS grade. CONCLUSION: With its improved diagnostic efficiency, the 90-min extended EMLA test can feasibly be used as an alternative to NCS, especially in general practice settings. Its potential clinical utility should be explored in a large population of CTS patients showing varying clinical and electrophysiological severities.