#3545 Ultrasound for median nerve evaluation in dialysis patients: a reliable tool for detecting carpal tunnel syndrome

Abstract Background and Aims Carpal tunnel syndrome (CTS) is a common complication in dialysis patients, primarily due to beta-2 microglobulin (β2M) amyloidosis and prolonged dialysis exposure. This study investigates dialysis vintage and modality, β2M levels, and CTS severity, using a CTS-6 score (a score >12 indicates ∼80% probability of CTS). Two ultrasound parameters were used to define CTS: a median nerve cross-sectional area (MN-CSA) cutoff of >11.5 mm² and a median nerve cross-section difference >2 mm², as measured at the pronator quadratus and carpal tunnel levels. Method This cross-sectional study included 105 dialysis patients (mean age: 62.4 ± 14.2 years). MN-CSA was measured bilaterally using a high-frequency linear probe at the level of both the pronator quadratus muscle and the carpal tunnel. β2M levels, dialysis vintage, and modality (hemodialysis [HD] vs. hemodiafiltration [HDF]) were recorded. The Mann-Whitney U test was used to assess group differences, presented as median and interquartile range (IQR). Clinical severity of symptoms was evaluated using the CTS-6 score, which considers tingling history in the median nerve innervation territory, thenar atrophy, two-point discrimination loss, and positive Phalen's and Tinel's signs. Spearman correlation analyses were performed. Statistical significance was set at P < 0.05. Results Clinical signs of CTS (CTS-6 score >12) were present in 19% of patients. Ultrasonographic signs of CTS were present in 10.5% of patients (MN-CSA >11.5 mm²) and 37.1% of patients (pronator quadratus–carpal tunnel difference >2 mm²). Patients with a CTS-6 score >12 had thicker median nerves on ultrasound (significantly higher indexed MN-CSA: median 5.22 [IQR unspecified] vs. 4.46 [IQR unspecified]; P = 0.024) and were older (73 years [IQR 15] vs. 64 years [IQR 17.75]; P = 0.045). HD patients had significantly higher CTS-6 scores than HDF patients (median 4.5 [IQR 9.5] vs. 4.0 [IQR 5]; P = 0.049) and exhibited thicker median nerves (MN-CSA indexed by body surface area: 4.75 [IQR 1.07] vs. 3.97 [IQR 1.5]; P < 0.01). The CTS-6 score positively correlated with indexed MN-CSA bilaterally (right: r = 0.21, P = 0.031; left: r = 0.34, P < 0.01) and with hypervolemia as assessed by Body Composition Monitor in both arms (right: r = 0.30, P = 0.002; left: r = 0.22, P = 0.023). Median nerve thickness showed a positive correlation with age (right: r = 0.38, P < 0.01; left: r = 0.41, P < 0.01) and a negative correlation with dry weight (r = –0.36, P < 0.01). β2M levels positively correlated with dialysis vintage (r = 0.26, P = 0.008) but did not correlate with nerve thickness or CTS. β2M levels did not differ significantly between CTS and non-CTS groups (P = 0.344), suggesting additional metabolic contributors to CTS pathogenesis in this population. Conclusion Ultrasound reliably detects median nerve enlargement in dialysis patients, correlating with CTS severity, dialysis modality, and fluid status. A CTS-6 score >12 was associated with thicker nerves, older age, and hypervolemia. Patients on HD had higher CTS-6 scores and greater nerve thickness than those on HDF, possibly alluding to the role of middle-molecule clearance. Although β2M levels correlated with dialysis vintage, they did not differentiate CTS status, suggesting other metabolic factors contribute to CTS risk. These findings reinforce indexed MN-CSA and the pronator quadratus–carpal tunnel difference (>2 mm²) as key ultrasound markers for CTS risk stratification.