Background/Objective:Recent emphasis on difficult-to-treat (D2T) Psoriatic Arthritis (PsA) lacks clarity in defining characteristics; this study aims to adress this gap.In this study, we aimed to determine the clinical and demographic characteristics of patients with difficult-to-treat PsA registered in the national health registry dataset.

Methods:Leveraging Big Data technology,the research harnessed the Turkish Ministry of Health’s E-Pulse database,housing clinical records for over 80 million individuals since 2016. In this analysis, instances of Psoriatic Arthritis (PsA) were identified through ICD-10 codes (M07, M09, and their subgroups), with cases defined as patients having the respective ICD-10 codes entered at least twice with a 30-day interval. For comorbidity analysis, comorbidity was considered to be present in patients with the same disease ICD-10 code entered at least 3 times without a time limit.Definition of D2T: The dificult to treat PsA was defined as PsA patients prescribed ≥2 different mechanisms with biologic disease-modifying anti-rheumatic drugs. (1) Demographics, comorbidities and treatment strategies were assessed in this group and comparisons were made between patients with only 1 bDMARD usage.

Results:From the cohort of 40.463 PsA patients 11.923 (29.4%) used at least one bDMARDs. Overall, 2.605 (6.4% of all PsA patients, 21.8% of patients using bDMARDs) were defined as difficult-to-treat PsA. The distribution of thegroups according to the number of drugs used was as follows: two bDMARDs n:2.524 (%21.2), three bDMARD n:1.138 (%9.5), four bDMARD n:455 (%3.8), ≥5 (%2.5).There were no differences in CTDs, glucose intolerance, hyperlipidemia, pulmonary or renal diseases, malignancies, or thrombosis between patients who used one bDMARD and patients who used two or more bDMARDs. On the other hand, neuropsychiatric disorders were more frequent in patients who used two or more bDMARDs [depression 32.3% vs 26.1%, OR 95% CI 1.35 (1.23-1.48), fibromyalgia 12.0% vs 7.5%, OR 95% CI 1.64 (1.42-1.89)]. Patients with difficult-to-treat PsA were more likely to use csDMARD and glucocorticoids (Table 1).

Conclusion:Approximately 6% of all PsA patients in the national health register and about one-fifth of patients on bDMARDs used two or more different mechanisms bDMARDs. The main determinant factor is the presence of depression and fibromyalgia, which is slightly higher in women. Although causality cannot be demonstrated according to our data, special care should be taken in this patient group.