Diagnostic potential of ultrasound in carpal tunnel syndrome with different etiologies: correlation of sonographic median nerve measures with electrodiagnostic severity

Background: Carpal tunnel syndrome (CTS) is the commonest entrapment neuropathy. The aim of this study was to assess the accuracy and validity of high resolution musculoskeletal ultrasound (US) in the diagnosis of CTS in the Saudi population. Methods: Sixty patients were diagnosed clinically to have CTS involving 89 wrists that were confirmed by neurophysiologic studies. Each affected wrist was characterized as idiopathic or associated with either diabetes mellitus or hypothyroidism and were assigned a severity grade based on results of neurophysiologic studies. Seventy-six healthy wrists from fifty age, sex and BMI matched healthy subjects were included in the control group. High resolution ultrasound (US) was performed to assess median nerve cross sectional area distal (CSAd) at the entry to the carpal tunnel and proximally (CSAp) at the level of pronator quadratus muscle with a further calculation of their difference (Delta CSA) and their mean average or CSAd+CSAp/2 (CSApd). Results: There was a significant difference between both groups regarding mean +/- SD of CSAd, CSAp, Delta CSA, and CSApd (p = 0.0001). A positive significant correlation was also found between the CSAd, Delta CSA and the CSApd measurements with neurophysiologic severity grade of CTS (P = 0.001). A Delta CSA threshold of 2.5 mm(2) showed the highest sensitivity and specificity to diagnose CTS in Saudis. Conclusion: High resolution ultrasound is a valid and accurate diagnostic modality in carpal tunnel syndrome and correlated to CTS severity. A Delta CSA greater than 2.5 mm(2) is considered a valid diagnostic value for CTS in our Saudi population. CTS in our patients with diabetes tend to have greater median nerve US measurement values.