The 6-item CTS symptoms scale: a brief outcomes measure for carpal tunnel syndrome

To develop a psychometrically appropriate brief symptoms measure of carpal tunnel syndrome (CTS). Preoperative CTS 11-item symptom severity and 8-item functional status scales from 693 patients (71% women) with CTS were subjected to exploratory factor analysis and item response theory (IRT) analysis yielding a revised CTS symptoms scale. A validation sample of 213 patients (68% women) with CTS completed the 11-item disabilities of the arm, shoulder and hand (QuickDASH), and the revised symptoms scale and 116 patients also completed the original CTS symptom severity scale (median interval 11 days). Of the 11 CTS symptom severity scale items, 2 items that on factor analysis associated with the functional status items were removed. After IRT recalibrations of the remaining symptom severity scale items, 2 non-fitting items were removed and 2 items were merged creating the 6-item CTS symptoms scale. Factor analysis showed one dominant factor explaining 58% of the variance. Reliability was high (Cronbach alpha = 0.86; IRT person separation reliability = 0.88). No item displayed significant differential item functioning. The 6-item CTS symptoms scale showed strong correlation with the QuickDASH (r = 0.70) and agreement with the original symptom severity scale (ICC = 0.80). The 6-item CTS symptoms scale has good reliability and validity and can be used to measure symptom severity and treatment outcome in CTS.