This is a cross-sectional multicenter study carried out in four tertiary rheumatological centers in Italy, each with expertise in the diagnosis and treatment of PsA. This served as a sub-analysis of the ASSIST Study [12].

In particular, according to the main study, inclusion criteria were:

patients who had received a diagnosis of PsA and who met the CASPAR (ClASsification criteria for Psoriatic Arthritis) criteria [13];

age ≥ 18 years;

patients with a follow-up period exceeding 12 months.

For each patient, the main demographic and clinical data were collected, which included sex, age, disease duration, subset of PsA (mono/oligo/polyarthritis), prevalent axial disease (according to the criteria proposed by ASAS for inflammatory back pain and/or radiological axial involvement) [14], prevalent enthesitis involvement and treatments. The clinical examination included: number of swollen (out of 66) and tender (out of 68) joints, presence of dactylitis, presence of psoriasis at the time of the visit, the body surface area (BSA), presence of enthesitis (assessed with the Leeds Enthesitis Index (LEI) [15], pain assessment on Visual Analogic Scale (VAS), patient (PtGA) and physician (PhGA) global assessment of disease activity on VAS [16]. The assessment of disease activity was performed by using the clinical Disease Activity index for Psoriatic Arthritis (cDAPSA)[17] and the Minimal Disease Activity (MDA) [18]. Function and disability were assessed through the Health Assessment Questionnaire-Disability Index (HAQ-DI) [19] and the EQ-5 questionnaire [20], while the impact of the disease through the Psoriatic Arthritis Impact of the Disease (PsAID-12) [21]. Finally, the Widespread Pain Index (WPI) was performed in all patients with PsA [22]. The WPI quantifies the extent of bodily pain on a 0–19 scale, by asking patients if they had pain or tenderness in 19 different body regions.

Assessment of patient–physician interaction

PEPPI and CollaboRATE questionnaires were used, respectively, to evaluate the patient’s perception of the patient–physician relationship and the shared decision-making process from the patients’ point of view. These two questionnaires were administered after a routine clinical examination in a separate room.

The PEPPI is a validated tool structured on five questions (in the short form used for this study) with a score ranging from 0 to 25, where higher scores represent a better perception of the patient–physician relationship [9, 10].

The CollaboRATE questionnaire is a validated tool structured on three questions with a score ranging from 0 to 9, where higher scores indicates more shared decision-making process [11]. A rheumatologist of our group (FMP) translated the questionnaires from English to Italian as a first draft and then sent to a mother tongue English speaker with a good knowledge of Italian but without any knowledge of either questionnaire. The mother tongue English speaker back-translated the Italian version of the questionnaire and no significant cultural adaptations were made.

All procedures were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration. Informed consent was obtained from all individual participants included in the study. The study was approved by the Institutional Review Board of the University of Molise (Prot. n. 17/2021), which covered all four tertiary rheumatological centers.

Statistical analysis

Descriptive statistics were used to summarize all the variables collected. Normal variables were expressed as mean and standard deviation (SD) and non-normal variables were expressed as median and inter-quartile range (IQR). Categorical variables were expressed as number (n) and percentage (%).

Correlation between the different continuous variables with the PEPPI and CollaboRATE questionnaires scores were assessed using the Spearman rho correlation index. Partial correlation was used to adjust results for continuous variables. The Kruskal–Wallis H test and the Mann–Whitney U test were used to compare medians. P values < 0.05 were considered significant.