Supplementary Material for: Carpal Tunnel Surgery as Proxy for Dialysis-Related Amyloidosis: Results from the Japanese Society for Dialysis Therapy

Background/Aims: This study aims to identify current risk factors for developing dialysis-related amyloidosis using carpal tunnel syndrome (CTS) as proxy for general amyloidosis. Methods: The cohort consisted of 166,237 patients on dialysis (mean age 66.1 ± 12.4 years; mean dialysis vintage 7.2 ± 6.4 years) who could be followed for a year between 2010 and 2011. Of these, 2,157 (1.30%) needed first-time CTS surgery during the study period. Odds ratios (ORs) for CTS were calculated at a 95% confidence interval (95% CI) after adjusting for age, gender, primary kidney disease, history of smoking, history of hypertension vintage, dialysis modality, use of high-flux membrane, body mass index, serum albumin, Kt/V, normalized protein catabolic rate, C-reactive protein, pretreatment β₂-microglobulin (β₂MG), and β₂MG clearance. Results: Adjusted ORs of first-time CTS for vintages 10-15, 15-20, 20-25 (referent), 25-30, and >30 years were, respectively, 0.18 (0.12-0.26), 0.43 (0.31-0.62), 1.00, 2.37 (1.64-3.40), and 3.87 (2.52-5.93). Adjusted ORs for ages 40-50, 50-60 (referent), 60-70, 70-80, and >80 were 0.53 (0.30-0.94), 1.00, 1.89 (1.41-2.52), 1.52 (1.08-2.14), and 1.04 (0.60-1.80). Female gender, low serum albumin, and diabetic nephropathy were also associated with CTS. Pretreatment serum β₂MG and β₂MG clearance <80% were not significant, although β₂MG clearance >80% was negatively associated with CTS [OR 0.34 (0.13-0.90)]. Conclusion: ORs of first-time CTS almost doubled with every 5-year increase in dialysis vintage. ORs of CTS were highest for patients aged 60-70. Other factors associated with CTS were gender, serum albumin, and diabetic nephropathy. β₂MG clearance >80% may decrease the incidence of CTS.