Development and testing of new candidate psoriatic arthritis screening questionnaires combining optimal questions from existing tools

Objective: Several questionnaires have been developed to screen for psoriatic arthritis (PsA) but head to head studies have found limitations. This study aimed to develop new questionnaires encompassing the most discriminative questions from existing instruments. Methods: Data from the CONTEST study, a head to head comparison of three existing questionnaires, were used to identify items with a Youden's index of ≥0.1. These were combined using four approaches: CONTEST- simple additions of questions; CONTESTw- weighting using logistic regression; CONTESTjt- addition of a joint manikin and CONTESTtree- additional questions identified by CART analysis. These candidate questionnaires were tested in independent datasets. Results: 12 individual questions with a Youden's index of ≥0.1 were identified but 4 of these were excluded due to duplication and redundancy. Weighting for two of these questions, was included in CONTESTw. Receiver operating characteristic (ROC) curve analysis showed that involvement in six joint areas on the manikin was predictive of PsA for inclusion in CONTESTjt. CART analysis identified a further 5 questions for inclusion in CONTESTtree. CONTESTtree was not significant on ROC analysis and discarded. The other three were significant in all datasets, although CONTESTw was slightly inferior to the others in the validation datasets. Potential cut points for referral are discussed. Conclusion: Of four candidate questionnaires combining existing discriminatory items to identify psoriatic arthritis in people with psoriasis three were found to be significant on ROC analysis. Testing in independent datasets identifies two questionnaires: CONTEST and CONTESTjt that should be pursued for further prospective testing.