Difficult-to-Treat Concept in Psoriatic Arthritis: Analysis of 2 Potential Definitions in a Large Group of Patients. A Cross-Sectional Study

Objective. The main aim of the study was to evaluate the performance of 2 proposed criteria for difficult-to-treat (D2T) psoriatic arthritis (PsA) in a group of patients and to evaluate the agreement between the 2 sets of criteria. Methods. We performed a cross-sectional analysis of 2 longitudinal cohorts of patients with PsA fulfilling the Classification Criteria for Psoriatic Arthritis (CASPAR), with at least 1 year of follow-up. A detailed medical history was collected and a physical examination was performed for all recruited patients. The proposed criteria for patients with D2T PsA were applied in our group. To test the performance of the 2 sets of criteria, we used an external validator (absence of patient acceptable symptom state + physician global assessment ≥ 6 cm). Finally, the agreement between the 2 sets of criteria was assessed. Results. We evaluated 378 patients with PsA (219 male/159 female), with a mean age (range) of 58 (19-75) years. Seventy-five (19.8%) patients fulfilled the D2T criteria proposed by Perrotta et al and 58 (15.3%) the D2T criteria proposed by Kumthekar et al. Both criteria showed comparable performance, with low sensitivity (Perrotta: 37.8%, Kumthekar: 29.7%) but good specificity (Perrotta: 82.1%, Kumthekar: 86.2%). Finally, the agreement between the 2 sets of criteria is substantial (Fleiss κ 0.72), suggesting that both criteria identify nearly the same group of patients. Conclusion. Our study compared 2 published sets of criteria showing comparable performance and substantial agreement. This study may pave the way for further research in this field.