PO:01:001 | Clinical and histopathological features of refractory psoriatic arthritis undergoing ultrasound-guided synovial biopsy: comparison between non-inflammatory and persistent inflammatory profiles

Marianna Tamussin¹, Carlo Garaffoni¹, Maria Capita¹, Serena Ceccato¹, Giovanni Lanza², Mariangela Salvato³, Kiren Khalid³, Francesca Frizzera³, Lorenzo Di Luozzo³, Annalisa Angelini⁴, Roberta Ramonda³, Alessandra Bortoluzzi¹, Andrea Doria³, Marcello Govoni¹, Alessadro Giollo³, Ettore Silvagni¹ | ¹Rheumatology Unit, Department of Medical Sciences, University of Ferrara and Azienda Ospedaliero-Universitaria S. Anna Ferrara, Italy; ²Pathology Unit, Department of Translational Medicine, University of Ferrara, Ferrara Ferrara, Italy; ³Rheumatology Unit, Department of Medicine , DIMED, University of Padua Padova, Italy; ⁴Cardiovascular Pathology, Department of Cardiac, Thoracic, Vascular Sciences and Pulic Health, University of Padua, Padova, Italy

Background. and purpose Psoriatic arthritis (PsA) is a chronic inflammatory arthritis associated with psoriasis that, similarly to rheumatoid arthritis (RA), can be challenging to treat in most patients. Literature defines 'refractory’ PsA variably, often including patients with multiple therapeutic failures. This study aims to evaluate the association between clinical, laboratory, ultrasound, and histopathological variables in patients with refractory psoriatic arthritis (Re-PsA), stratified according to proposed definitions of Persistent Inflammatory Psoriatic Arthritis (PiPsA) and Non-Inflammatory Psoriatic Arthritis (NiPsA) phenotypes.

Materials and Methods. In this prospective, multi-centre, cohort study, we included patients with Re-PsA, defined as failure of at least one b/tsDMARD, who underwent ultrasound-guided synovial biopsy between 2019 and 2024 at two tertiary-referral centers. Baseline demographic, clinical, laboratory, ultrasound, and histopathological data, — including the Krenn synovitis score (KSS), — were collected and analyzed using t-tests, Wilcoxon rank-sum tests, and chi-square tests, when appropriate. Classification into NiPsA or PiPsA was based on definitions from Zabotti et al. (PiPsA: imaging evidence of ongoing inflammation in at least one joint or tendon sheath (based on ultrasonography or MRI), and MATRIX-D2T study (PiPsA: Physician Global Assessment (PhGA)>20/100 and CRP>0.5 mg/dL at baseline, NiPsA: PhGA<=20 or CRP<=0.5 mg/dl).

Results. 29 patients with Re-PsA were recruited; 15/29 (52%) were male, with a mean (SD) age of 60 (9) years and a mean (SD) disease duration of 14 (9) years. Table 1 summarizes baseline characteristics. According to Zabotti et al.'s definition, 23/29 patients were classified as PiPsA, while 19/28 met PiPsA criteria according to MATRIX-D2T’ definition. A high number of tender joints (p = 0.005) and elevated baseline inflammatory markers (ESR p=0.006, CRP p<0.001) were significantly associated with PiPsA forms, according to Zabotti et al. and MATRIX-D2T definitions, respectively. The association with inflammatory markers was expected under the MATRIX-D2T definition but was not observed with Zabotti et al.'s one, where, unexpectedly, mean inflammatory marker levels were higher in patients classified as NiPsA. Neither disease duration nor ultrasound features of the biopsied joint (grey scale, effusion, and power Doppler) were significantly associated with PiPsA in either definition. Based on Zabotti’s definition for PiPsA, the Krenn inflammatory infiltrate score was significantly higher (median (IQR) 2.00 (2.00, 3.00) vs 1.00 (1.00, 2.00), p=0.031). Moreover, as shown in Figure 1, persistently inflammatory forms tended to have higher KSS levels according to both definitions.

Conclusions. Despite the lack of universally accepted definitions for PiPsA and NiPsA, our study shows a substantial heterogeneity in the clinical variables across current definitions. KSS may contribute to a potential composite definition of refractory PsA, as higher synovial Krenn inflammatory infiltrate score was significantly associated with persistently inflammatory forms according to the definition by Zabotti et al.