Clinical and Ultrasound Characteristics of a Difficult-to-Treat Psoriatic Arthritis Population

<b>Background:</b> Achieving low disease activity or remission in psoriatic arthritis (PsA) remains difficult. The GRAPPA group recently defined difficult-to-treat (D2T) PsA but did not include a time-based criterion. <b>Objectives:</b> This study aimed to evaluate the prevalence and features of D2T PsA using several operational definitions. <b>Methods:</b> A cross-sectional study at a tertiary center enrolled PsA patients with active disease confirmed by clinical exam and ultrasound. D2T PsA was defined by: (1) failure of ≥1 csDMARD plus ≥2 b/tsDMARDs with different mechanisms of action (GRAPPA definition); (2) ≥2 b/tsDMARDs with different mechanisms of action within 12 months (time-based definition); or (3) failure of >3 b/tsDMARDs with different mechanisms of action (very refractory). Clinical, demographic, radiographic, and ultrasound data were analyzed, and multivariable analyses identified independent associations. <b>Results:</b> Seventy-two patients (54.2% female, median age 56, disease duration 84 months) all had active disease (median DAPSA 17); 68% had comorbidities. Enthesitis, dactylitis, and nail disease were seen in 20.8%, 45.8%, and 41.7%. HLA-B27 positivity was 13.9%. Radiographic erosions and ultrasound paratenonitis were present in 37.5% and 33.3%. GRAPPA D2T criteria were met by 23.6%, linked to longer disease duration, higher activity, HLA-B27, comorbidities, and combined therapy. Time-based D2T (12.5%) showed higher DAPSA and nail involvement, with ultrasound paratenonitis and combined therapy independently associated. Very refractory patients (11.1%) only correlated with combined therapy. <b>Conclusions:</b> Up to one-fourth of PsA patients remain active despite multiple treatments. D2T PsA is associated with disease duration, comorbidities, activity, HLA-B27, combined therapies. Remarkably, patients who fulfilled the <12-month D2T definition were more likely to present with nail involvement and ultrasound-detected paratenonitis.