Comprehensive Sonographic Paradigm and Trend Pattern of Median Nerve Indices in Carpal Tunnel Syndrome from Wrist to Forearm: What We Need to Know

<b>Objective:</b> The study aim was panoramic sonographic inspection of the median nerve (MN) from the wrist to the forearm in cases and controls. Additionally, integration of comparisons at various levels may aid in identifying principal ultrasound parameters of carpal tunnel syndrome (CTS). <b>Methods:</b> Dynamic, static, and panoramic sonographies of 65 healthy and 83 CTS hands were performed. Multileveled qualitative (MN and flexor retinaculum morphology) and quantitative (cross-sectional area CSA, differences, and ratios) MN variables for CTS, followed by comparative statistical analysis to predict values and patterns of MN, were derived. <b>Results:</b> Subjectively, hypoechoic, vascular, compressed, hypomobile MN and bowed thickened flexor retinaculum were significantly more prevalent in cases (28.9-66.3%) than in controls (0-7.7%). Objectively, the proximal to inlet (pi) and the forearm at 12 cm (12) were the most representative sites. The area under curve (AUC) values for the MN dimensions, in decreasing order, were 0.9, 0.89, 0.86, and ≤0.80 for the CSA difference 'pi' and '12' (Cpi-C12), the CSA proximal to inlet (Cpi), the ratio of CSA at pi and 12 (Cpi/C12), and the CSA at inlet (Ci), respectively. Their cut-off values were 3.7, 9.1, 1.8, and 7.2 mm², respectively. Differences and ratios between 'Cpi' and 'Ci' were less reliable (AUC ≤ 0.74, sensitivity ≤ 61.4%). Flexor retinaculum bowing, thickening, and MN flattening ratios were unreliable. <b>Conclusions:</b> Sensitivity, specificity, and precision of MN sonographic parameters in CTS increase by utilizing differences and ratios between wrist and forearm rather than isolated values. The recommended site in wrist is proximal to the inlet, and in the forearm, the best site to determine ratios and differences is at 12 cm from the distal wrist crease.