Measuring symptoms severity in carpal tunnel syndrome: score agreement and responsiveness of the Atroshi-Lyrén 6-item symptoms scale and the Boston symptom severity scale

PURPOSE: To assess score agreement between the Atroshi-Lyrén 6-item symptoms scale and the Boston 11-item symptom severity scale and compare their responsiveness in patients with carpal tunnel syndrome before and after carpal tunnel release surgery. METHODS: This prospective cohort study included 3 cohorts that completed the A-L and Boston scales (conventional score 1–5) on the same occasion: a preoperative and short-term postoperative cohort (212 patients), a mid-term postoperative cohort (101 patients), and a long-term postoperative cohort (124 patients). Agreement was assessed with Lin’s concordance correlation coefficient and Passing-Bablok regression analysis. Analyses using item response theory were conducted on responses from the preoperative/short-term postoperative cohort including testing of item infit/outfit. Reliability was assessed with Cronbach alpha. Overall and sex-specific effect sizes were calculated using Cohen’s d. RESULTS: Lin’s CCCs were high (0.81–0.91). Passing-Bablok analysis showed constant and proportional differences in all cohorts except preoperative to short-term postoperative change. Both scales showed high reliability (alpha, 0.88–0.93). The IRT-based analyses showed infit/outfit values within the desired range. With IRT-based scoring, the A-L scale had significantly higher responsiveness than the Boston scale, overall (d, 2.02 vs 1.59), in women (d, 2.22 vs 1.77) and in men (d, 1.74 vs 1.36). CONCLUSION: The Atroshi-Lyrén 6-item symptoms scale and the Boston 11-item symptom severity scale show good agreement but are not equivalent in measuring CTS-related symptoms severity. When using IRT-based scoring, the Atroshi-Lyrén scale demonstrated significantly higher responsiveness. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11136-021-03039-1.