Background Prompt diagnosis and treatment of psoriatic arthritis (PsA) are essential to reduce the risk of permanent joint damage. Although composite measures established in rheumatoid arthritis are often used in PsA for monitoring disease activity, their utility as an aid to identification of PsA, compared to the utility of other features of PsA such as dactylitis and enthesitis, has not been established.
Objectives To compare various clinical assessments in their ability to diagnose PsA in a post-hoc analysis of findings from the PREPARE study, a multicenter non-interventional study conducted to estimate PsA prevalence in patients with psoriasis.
Methods Consecutive psoriasis patients seen in dermatology centers were evaluated by rheumatologists to establish/exclude a clinical diagnosis of PsA based on physical examination, medical history, and laboratory findings. With the latter diagnosis serving as the standard for comparison, several rheumatologic signs/symptoms/indexes were assessed. The cutoff value for each assessment that best corresponded to the clinical PsA diagnosis was obtained by maximizing sensitivity plus specificity in receiver operating characteristic (ROC) analyses. Kappa (K) coefficient analyses determined the level of agreement between the clinical PsA diagnosis and assessment cutoffs (1=perfect agreement).
Results Of 949 psoriasis patients assessed by rheumatologists, 285 (30%) had PsA based on clinical diagnosis (95% CI: 27%, 33%). Results varied from dactylitis in ≥1 joint, a cutoff with low sensitivity and high specificity, to a tender joint count of ≥1, a cutoff with surprisingly high sensitivity and specificity in lower and upper extremities (Table). K values were modest for all cutoffs. Of the composite tools, DAS44 (including foot joints) performed better than DAS28.
Conclusions In this large prevalence study, nearly one third of psoriasis patients seen in dermatology centers received a clinical diagnosis of PsA by a rheumatologist. Although a statistically significant level of agreement was observed between the clinical PsA diagnosis and the cutoffs for the various assessment tools analyzed, none of the K values were high, suggesting that clinicians may be using combinations of recorded features with or without unrecorded features to make the diagnosis.
Acknowledgements This study was sponsored by Pfizer Inc. Medical writing support was provided by Donna McGuire of UBC Scientific Solutions and was funded by Pfizer Inc.
Disclosure of Interest P. Helliwell Speakers bureau: Pfizer, O. FitzGerald Grant/research support from: Abbott, BMS, Pfizer, MSD, Consultant for: Abbott, UCB, Pfizer, Speakers bureau: Abbott, Pfizer, MSD, D. Alvarez Shareholder of: Pfizer Inc, Employee of: Pfizer Inc, A. Szumski Consultant for: Pfizer Inc, H. Jones Employee of: Pfizer Inc