Objective: To develop a psychometrically appropriate brief symptoms measure of carpal tunnel syndrome (CTS).
Methods: 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).
Results: 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).
Conclusion: The 6-item CTS symptoms scale has good reliability and validity and can be used to measure symptom severity and treatment outcome in CTS.