Introduction

Psoriatic arthritis (PsA) is a chronic inflammatory arthritis estimated to affect up to 42% of psoriasis patients and 0.056% to 0.28% of the general population [1,2]. It is a heterogeneous disease that manifests in various articular patterns and other musculoskeletal features extending beyond inflammatory arthritis, like enthesitis and dactylitis [3]. The distinct phenotypic articular subtypes were first described by Wright and Moll in 1973 as classification criteria of the disease, which include asymmetrical oligoarthritis, symmetrical polyarthritis, distal interphalangeal (DIP) joint involvement, axial disease, and arthritis mutilans [4]. Subsequently, several classification criteria were further evolved to recognize other hallmark extra-articular features of PsA, like enthesitis and dactylitis [5–7]. Recognizing the different manifestations of the disease is crucial for understanding their impact on the overall disease burden. This multifaceted disease can lead to permanent joint damage, increase the rate of work disability, and poor quality of life. Additionally, it contributes to notable psychological stress and depression and, potentially, decreased life expectancy [8,9].

The emergence of effective novel therapies has positively impacted the clinical course of PsA and its outcomes. Notwithstanding these significant therapeutic advancements, most evidence of their efficacy is based on clinical trials that predominantly target a specific PsA subgroup, namely those with polyarticular disease [10]. This was highlighted in a previous systemic review conducted by our research group [11], which reviewed relevant clinical trials and found that all shared the same inclusion entry criteria for the assessment of their primary endpoint, which was the peripheral joint counts with a primary requirement of at least five joints or, in fewer studies, three joints. None of the clinical trials had prespecified other PsA subtypes, such as DIP joint, axial disease, and arthritis mutilans, or non-articular manifestations like enthesitis and dactylitis, nor their specific outcome measures in their primary endpoint. Instead, these were addressed as exploratory outcomes. Due to this underrepresentation, the efficacy of the therapeutic agents for these subgroups is challenging to ascertain. As a result, their access to different treatment options has also been limited. In addition to these concerns, many phase III clinical trials lack long-term follow-ups and do not involve disease burden data. These clinical trials typically exclude patients with major comorbidities, making the studies less representative of real-world settings. Overall, important evidence gaps remain regarding real-world treatment effectiveness, phenotype-specific outcomes, and patient-centered outcomes in routine clinical practice. Longitudinal real-world registries are therefore needed to better understand disease heterogeneity, treatment trajectories, and predictors of clinical outcomes across diverse PsA populations.

“The Ontario Best Practices Research Initiative (OBRI)” is a provincial registry established in 2008 through the collaborative efforts of rheumatologists, patients, and researchers to improve the quality of care and health outcomes for rheumatoid arthritis patients in Ontario by gathering long-term information on therapies, clinical practice, and health care utilization in the real-world [12]. Building on this foundation, we developed the Observational Best Practices Research Initiative (OBRI-PsA) nationwide registry to include patients with PsA. This collaborative research program utilizes the existing OBRI platform registry to recruit PsA patients, mostly from community clinics, allowing for a deeper understanding of real-world practices and their impact on clinician and patient-reported outcomes. The registry was designed with the following long-term scientific objectives:

• to characterize demographic, clinical, and phenotypic heterogeneity in PsA across routine clinical care settings.
• to evaluate real-world treatment patterns, treatment persistence, and effectiveness of advanced therapies across PsA phenotypes.
• to assess longitudinal outcomes, including disease activity, physical function, quality of life, work productivity, healthcare utilization, and achievement of treatment targets such as minimal disease activity.
• to identify predictors of treatment response, treatment discontinuation, and long-term patient outcomes.
• and to evaluate healthcare practice variation, post-marketing treatment surveillance, and the impact of biosimilar switching in routine care.

This manuscript presents the initial descriptive report of the OBRI-PsA registry, including its rationale and protocol, alongside preliminary 18-month follow-up data describing the demographic, clinical, phenotypic, and treatment characteristics of the first enrolled patients, while demonstrating the feasibility and structure of the registry platform.

Methods

The OBRI-PsA registry is an ongoing, prospective, long-term, multicenter observational study that recruited its first patient on February 10, 2022, at nine rheumatology centers across Ontario, most of which are community-based. To enhance geographic representation and enable interprovincial comparisons, the registry expanded in 2024 to include one center each in British Columbia and Alberta and continues to recruit additional rheumatology sites across Canada. The study protocol was approved by the University Health Network Research Ethics Board (REB; No. 20-5639), where the registry is managed. Written informed consent was obtained from all participating patients before enrollment. See S1 Protocol for details.

The inclusion criteria require a diagnosis of PsA by a rheumatologist, with an active disease state determined by the treating rheumatologist and defined as necessitating a new therapy, including conventional synthetic disease-modifying antirheumatic drugs (csDMARDs), biologic agents, or targeted synthetic DMARDs (b/tsDMARDs). The definition of active disease places no threshold limitations on the domains (e.g., active joints and entheses counts, axial disease, skin severity, or inflammatory bowel disease (IBD)); it is solely based on the necessity for initiating new therapy for any indication, regardless of whether the treatment was ultimately initiated. Exclusion criteria included inability to attend scheduled follow-up assessments or situations in which standardized study data could not be reliably collected in English, either directly or with translator assistance, due to the use of English-language case report forms and centralized follow-up procedures. This criterion was applied to ensure data quality and consistency and did not represent exclusion of patients based on language, ethnicity, or race.

Baseline and follow-up data will be collected over 10 years through a prespecified protocol, and Case Report Forms (CRFs) by the rheumatologists during their routine clinical visits and trained telephone interviewers from the OBRI data management center to collect patient-reported outcomes. At baseline, phenotype data distinguished between historically ever-present disease manifestations and currently active disease domains at enrollment. Historical phenotypes (e.g., axial disease, enthesitis, DIP involvement, or polyarticular disease) were recorded based on treating rheumatologist documentation and clinical history without centralized prespecified classification criteria. In contrast, currently active disease domains reflected the clinical indication for therapy initiation or change at enrollment as determined by the treating rheumatologist. Active manifestations did not require predefined minimum thresholds, and patients could have overlapping active disease domains. Nonetheless, clinicians were required to support active disease assessments using routine clinical and objective measures when applicable, including tender and swollen joint counts, SPARCC enthesitis index, BASDAI/BASFI assessments, and, if axial disease activity was confirmed by imaging.

The timing of the routine clinical follow-up is left to the discretion of the treating rheumatologist. Follow-up telephone interviews from the OBRI data management center are conducted within two weeks of the new therapy and then at prespecified, regular intervals afterward (twice yearly). As patients were enrolled into the registry at different time points, lower patient numbers at later follow-up visits in the current descriptive analysis reflect that many patients had not yet reached those scheduled visits at the time of data extraction, rather than true loss to follow-up.

The following core study variables are assessed per patient at baseline and follow-up: clinical phenotype and active domains of the disease, routine laboratory assays, inflammatory markers, HLA-B27 testing, Axial MRI, X-ray of the peripheral joints to assess new bone formation and erosions (the last three investigations to be collected if done in standard of care), disease activity measures including the Disease Activity in Psoriatic Arthritis (DAPSA), Bath Ankylosing Spondylitis Functional Index (BASFI), Composite Psoriatic Disease Activity Index (CPDAI), Psoriatic Arthritis Disease Activity Score (PASDAS), Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Ankylosing Spondylitis Disease Activity Score (ASDAS), dactylitis counts, Spondyloarthritis Research Consortium of Canada (SPARCC) enthesitis index, Assessment of Spondyloarthritis International Society (ASAS) partial remission criteria (axial disease), and Psoriatic Arthritis (PsA) minimal disease activity (MDA) criteria, patient-reported outcomes, new or existing comorbidities, treatment details, and adverse effects.

Results: Preliminary 18-month analysis

Baseline demographics, clinical characteristics, and disease phenotypes

As of September 2024, the OBRI-PsA registry had enrolled 101 patients. Table 1 presents the characteristics of the participants at the time of enrollment. The mean age of the participants was 53.9 ± 12.7, with 61.4% being female. Historically ever-present disease manifestations included symmetrical polyarthritis, seen in 86.1% of participants, while DIP involvement occurred in 45% of participants. In contrast, axial disease and asymmetrical oligoarthritis were less common, reported in 23% and 15.8% of patients, respectively. None of the recruited participants had arthritis mutilans. Additionally, extra-articular features were prevalent in our cohort, with 91% of patients having skin psoriasis, 50% nail psoriasis, and enthesitis and dactylitis affecting 49% and 42%, respectively. At baseline, the most frequently reported comorbidities included hypertension (35%), anxiety (30%), depression (28%), and diabetes mellitus (25%), reflecting the known cardiometabolic and psychological burden associated with psoriatic arthritis.

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Table 1. Demographic and baseline clinical characteristics and comorbidities (N = 101).

https://doi.org/10.1371/journal.pone.0352264.t001

Baseline disease activity and functional assessment

The patients’ mean (± SD) total tender joint count was 9.8 ± 8.9, while their mean (± SD) total swollen joint count was 6.5 ± 5.5. The mean (± SD) total pain score was 5.9 (± 2.6), and the patient global score was 5.7 (± 2.3). Additionally, the mean (± SD) psoriasis percentage body surface area was 3.3 (± 7), and their enthesitis score, measured by the SPARCC enthesitis index, was 1.9 (± 3.1). The mean (± SD) HAQ was 0.84 (± 0.67), with 28% of patients meeting the fibromyalgia criteria. [13] Patients with jobs outside the home reported missing 14% of working days and experienced a 28% impairment while working. Further findings on baseline activity, functional, and work productivity measures are summarized in Table 2.

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Table 2. Disease activity and patient-reported assessments at enrollment, N = 101.

https://doi.org/10.1371/journal.pone.0352264.t002

Follow-up outcomes and treatment changes

Eighty-four participants completed the six-month follow-up, while 54 and 45 patients reached their 12- and 18-month follow-ups, respectively. Over time, disease activity measures summarized in Table 3 generally showed progressive improvement compared to baseline values. Patient-reported pain scores exhibited a notable reduction at each follow-up, with the most significant improvement observed at 12 months, decreasing from a baseline mean (± SD) of 5.8 (± 2.5) to 3.0 (± 2.5). Similarly, mean (± SD) physician global assessments displayed a steady trend of improvement, with scores decreasing from 4.8 (± 2.0) to 2.0 (± 1.7) at 12 months and from 5.2 (± 2.1) to 2.3 (± 2.2) at 18 months. Additionally, SPARCC enthesitis index scores and psoriasis skin surface area percentages showed a pattern of improvement over time. However, there was a trend toward worsening in most measures at month 18 compared to month 12, although values remained improved relative to baseline. Importantly, by 18 months, only one-third of patients overall had achieved the MDA target, and the rates varied significantly by phenotype (Fig 1). The proportion of patients achieving MDA varied considerably: 62.5% with mono-oligoarthritis, 52.6% with DIP joint involvement, 38.5% with axial disease, 35.0% with skin-predominant psoriasis, 30.8% with polyarthritis, and 24.0% with enthesitis. (Refer to S4 and S5 Tables and S1 Fig for detailed longitudinal outcomes).

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Table 3. Disease activity measures of psoriatic arthritis patients at each follow-up visit.

https://doi.org/10.1371/journal.pone.0352264.t003

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Fig 1. Proportion of patients achieving minimal disease activity by phenotype at enrollment and follow-up.

Numeric values are provided in the S6 Table.

https://doi.org/10.1371/journal.pone.0352264.g001

During follow-up, although only 37% and 33% of patients achieved MDA at 12 and 18 months, respectively, the majority remained on their initial therapy, while a smaller proportion required treatment adjustments (Fig 2). Overall, 60–74% of patients maintained their treatments at 6, 12, and 18 months, whereas 19–30% of patients required a change in their medications due to ongoing disease activity. Consistent with baseline data, the primary reasons for treatment changes were active peripheral arthritis and skin psoriasis.

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Fig 2. This bar chart illustrates reasons for patient treatment modifications at different follow-up periods (6, 12, and 18 months).

The percentage of patients within each treatment decision category is displayed for each time point.

https://doi.org/10.1371/journal.pone.0352264.g002

Subset analysis

Outcome measures in fibromyalgia patients.

In our study, 28% of patients met the clinical diagnostic criteria for fibromyalgia. Similar to the general population, 74% of patients with fibromyalgia were female. When compared to non-fibromyalgia patients, these individuals were diagnosed with PsA at a younger age, with a mean (± SD) of 40.5 (±14.9) years compared to 45.5 (±13.1) years. Moreover, patients with fibromyalgia had higher disease activity scores across multiple domains. They reported a higher mean (± SD) tender joint count of 14.0 (±11.9) vs. 8.6 (±7.3), swollen joint count of 7.4 (±6.1) vs. 6.2 (±5.2), SPARCC enthesitis index of 4.2 (±4.4) vs. 1.1 (±1.9), and patient global assessment of 6.9 (±1.9) vs. 5.2 (±2.3), suggesting a greater disease burden. However, this may be subjective, as the mean (± SD) physician’s global assessment was only mildly higher than the non-fibromyalgia group with a mean of 5.6 (±1.7) vs. 4.6 (±2.1).

In addition to the heightened clinical burden, the impact of fibromyalgia extended beyond disease activity measures. Patients with fibromyalgia experienced a significant impact on their daily life and productivity. On average, they reported missing twice as many days of household work and experienced greater reductions in productivity. Furthermore, their social and leisure activities were also affected, as fibromyalgia patients missed an average of 8 days per month compared to 3 days for non-fibromyalgia patients. Baseline demographics and clinical characteristics of patients with fibromyalgia are summarized in Table 4.

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Table 4. Baseline demographics and clinical characteristics of fibromyalgia vs. non-fibromyalgia patients.

https://doi.org/10.1371/journal.pone.0352264.t004

In addition to differences in disease burden, follow-up data revealed distinct treatment patterns among patients with and without fibromyalgia. At 6-month follow-up, 52% of patients with fibromyalgia had changed therapy due to suboptimal disease control compared with 22% of patients without fibromyalgia. Furthermore, none of the fibromyalgia cohort de-escalated therapy due to remission, in contrast to 7% of the non-fibromyalgia cohort who reduced therapy following remission.

Enrollment demographics and disease activity by sex.

Our registry revealed sex-based differences in clinical presentation, disease burden, and treatment indications. Enthesitis was more frequent among female patients (53% vs. 41%), whereas dactylitis (37% vs. 49%), nail psoriasis (40% vs. 67%), and inflammatory bowel disease (10% vs. 2%) were more common among male patients. Additionally, females appeared to have a higher disease burden, characterized by greater counts of tender and swollen joints, as well as higher enthesitis scores. Despite this, their patient- and physician-reported outcomes were only marginally lower. Moreover, female patients were noted to have a greater impact on their household responsibilities and social life. Notably, the primary reasons for initiating treatment were similar across both groups, except for nail psoriasis, which was more frequent in males compared to females (15% vs. 6%). (Refer to S6 Table for detailed sex-based differences.)

Discussion

The OBRI-PsA is a nationwide registry established to collect long-term longitudinal data, providing insights into diverse clinical phenotypes, treatment patterns, effectiveness, drug survival, and safety. It also aims to evaluate the impact of PsA on health services utilization. These insights could promote personalized medicine while enhancing resource allocation and cost-effectiveness in PsA care.

This study presents preliminary data on the clinical characteristics and treatment patterns of PsA patients enrolled in our ongoing registry. Our analysis indicated that 86% of our PsA cohort had a history of polyarticular disease involvement, and peripheral arthritis was the main indication for therapy initiation at enrollment in 93% of cases, a rate significantly higher than what is often observed in other registries of both early and established PsA and in clinical trials [14–19]. Furthermore, axial disease, enthesitis, and dactylitis were frequently reported, with prevalence rates aligning with other studies despite variations in the literature. This discrepancy may reflect differences in inclusion criteria, as unlike trials requiring ≥ 3–5 swollen joints, OBRI-PsA enrolls patients with minimal articular involvement or extra-articular activity (e.g., enthesitis, dactylitis). This inclusive approach captures a broader spectrum of real-world clinical settings, particularly those historically underrepresented in clinical trials, such as individuals with oligoarticular or isolated axial diseases. In addition, the predominance of polyarticular disease in our registry may also signal evolving diagnostic advancements, imaging, or a shift toward earlier recognition of PsA in community settings.

The OBRI-PsA study demonstrates that treatment modifications are associated with improvements in both patient- and physician-reported outcomes, as reflected in reductions in overall pain scores, and improvements in disease activity parameters. However, despite notable improvement, only one-third of our cohort achieved MDA at the end of 18 months of follow-up. More importantly, the proportion of patients achieving MDA varied across phenotypes, underscoring the need to examine drug effectiveness and response according to dominant phenotype—an area that remains understudied in current randomized controlled trials. Also the majority of the patients remained on the same treatment without modification, despite not achieving MDA, which shows that the treat-to-target approach is not widely utilized by our study sites. This warrants further investigation into potential explanations, including treatment target expectations, confounding or coexisting inflammatory conditions associated with difficult-to-treat disease, and limitations in drug access. The ongoing monitoring of treatment patterns in this registry will provide valuable insights into real-world evidence, facilitating informed treatment decisions in clinical practice. Future analyses include integrating clinical data with healthcare administrative databases, such as hospitalizations, emergency department visits, specialty care, and other health services, to shed light on the economic burden of the disease. This is an important aspect to address in strategizing cost-effectiveness in overall patient care.

In the context of optimizing treatment outcomes, it is equally important to consider comorbid conditions that may influence disease assessment and management, particularly fibromyalgia. This study shows trends of increased disease burden in patients meeting fibromyalgia criteria compared to those who did not. These patients exhibited higher counts of tender and swollen joints and increased entheseal involvement, as noted by the significantly higher SPARCC index in the fibromyalgia group. Moreover, despite similar rates of psoriasis surface body area in both groups, fibromyalgia patients had a greater impact of their skin disease, as noted by a significantly higher psoriasis symptom inventory. The overall symptomatic burden and reduction in quality of life may contribute to challenges in treatment adherence and response over time. In our cohort, patients with fibromyalgia were more likely to change therapy due to uncontrolled disease (52% vs. 22%) and were less likely to de-escalate treatment due to remission (0% vs. 7%). These observations further reinforce existing evidence of the interplay between PsA and fibromyalgia. Research by Elsawy et al.[20] and Ulutatar et al. [21] has reported fibromyalgia prevalence rates among PsA patients of 38.3% and 64%, respectively, which also demonstrated higher pain and enthesis scores and a reduced quality of life. These findings suggest that fibromyalgia not only affects patient-reported outcomes but may also confound inflammatory activity assessment, influencing long-term management of PsA and potentially leading to additional treatment adjustments that may not be warranted. Therefore, it is important to emphasize that unless fibromyalgia is addressed as part of the overall disease management strategy, patients in this group may never achieve controlled disease. We also observed that disease characteristics varied by sex. Notably, in our cohort, female patients generally exhibited higher clinical disease activity, especially in arthritis and enthesitis, compared to male patients. They also experienced greater overall disease burden, impacting work, household productivity, and social participation. These findings underscore the importance of including sex-sensitive approaches in disease management and support strategies.

Although our study has several strengths, the preliminary descriptive data have some limitations. This is a descriptive observational study with a relatively small sample size and an inherent risk of missing data, limiting our ability to infer causality or evaluate treatment effects.

A limitation of this registry is that eligibility for active disease was based on the treating rheumatologist’s clinical judgment without predefined disease activity thresholds or standardized training across sites. As a result, there may have been differences between clinicians in how active disease was assessed and reported. However, this pragmatic approach reflects routine clinical practice and may improve the generalizability of the registry findings.

In addition, although translator-assisted participation was permitted, reliance on English-language data collection tools may limit generalizability and will be addressed in future registry phases through multilingual instruments.

Another important limitation is that our study did not incorporate inflammatory biomarkers or imaging assessments as outcomes, which would generally have provided a more objective assessment of disease progression. Finally, despite important signals suggesting that fibromyalgia may influence disease activity assessment and treatment patterns in this cohort, it is important to acknowledge that fulfilment of fibromyalgia classification criteria does not necessarily equate to a confirmed clinical diagnosis. As classification-based assessments were used without formal clinical confirmation, the prevalence of fibromyalgia may have been overestimated in some patients. Addressing these limitations as our registry expands will improve the validity and reliability of the study.

Conclusion

This preliminary analysis from the OBRI-PsA registry highlights that, despite clinical improvements, only one-third of patients achieved MDA, with variable responses across phenotypes. Comorbid fibromyalgia was common and may have contributed to suboptimal control. Ongoing registry expansion will enable deeper evaluation of phenotype-specific responses, the influence of demographics and comorbidities, and the broader healthcare and economic impact.

Supporting information

Acknowledgments

We would like to acknowledge all OBRI-PsA participants and the following investigators: Vandana Ahluwalia, Nadir Khalidi, Sankalp Bhavsar, Jonathan Chan, Nancy Maltez, Reza Mirza, Rajwinder Dhillon, Sherry Rohekar, Elliot Hepworth, Catherine Ivory, Raman Joshi, Olga Ziouzina, Melissa Holdren, Faiza Khokhar, Pooneh Seyed-Akhavan, Ola Wierzbicki, Matthew Wong-Pack, and Bindee Kuriya, and their dedicated research teams, as well as the patients whose commitment and ongoing participation made this registry and study possible. Their contributions are central to advancing our understanding of the disease and improving future outcomes. We are especially grateful to Jennifer Boyle for her invaluable role as a patient representative, ensuring the integration of patient perspectives throughout the study. We also thank the Clinical Advisory Committee (CAC), co-investigators, and site-level collaborators for their leadership and sustained support. Special thanks to our data management team, including Carol Mously, and the interviewing team for their critical efforts in ensuring data quality, integrity, and patient-centered engagement.