This is the first Brazilian study using data only from SUS to delineate the population’s epidemiological characteristics in follow-up at the public health system care for PsA. We observed in this study an increase in both the prevalence and the incidence of visits that presented the PsA code of the ICD-10 in the last 14 years, showing a great variability between regions, an increased prevalence in women, and a large number of associated comorbidities.

A meta-analysis published in 2018 [6] showed a global prevalence of PsA of 133 per 100,000 people or 0.13% of the global population. In this study, we found a much lower prevalence in Brazil compared to the rest of the world. Although only patients who consulted for PsA in SUS were included, this is likely not the main reason for the difference found since several factors may account for this lower prevalence, such as genetic differences between populations, given that Brazil has a predominantly non-Caucasian population. Moreover, global differences in the PsA prevalence have already been demonstrated, with a higher prevalence in Caucasians [12, 13] and a lower prevalence in Asians [14, 15] and in Indigenous peoples of the Americas [16]. The Brazilian national prevalence in our study was close to that in Argentina [8] in 2011.

Previous studies on the national prevalence of PsA analyzed outpatient data, especially among patients in follow-up for psoriasis at outpatient clinics for the treatment of spondyloarthritis [17,18,19], and there was no study regarding the epidemiological characteristics of PsA analyzing data from the entire national territory.

Another factor that may have contributed to the lower prevalence was diagnostic error, which is common in PsA patients [2]. A meta-analysis published in 2015 [20] demonstrated that diagnostic error in this disease is due not only to confusion with other arthropathies (gout, rheumatoid arthritis, ankylosing spondylitis) but also to the absence of a gold standard test.

The difficult access to health services and specialized care in Brazil, as in other developing countries [21], is certainly the greatest limitation for the diagnosis of PsA, contributing to the difference found between regions. The South and the Southeast regions of Brazil have more physicians per person, more health services, more specialists, and higher Human Development Indexes [22], which may explain the greater offer of healthcare services as well as the greater demand for these services, consequently favoring early and accurate diagnoses.

A higher proportion of patients with PsA was found in the states of the South, Southeast, and Midwest regions (Fig. 1). This finding is consistent with a recent study on the prevalence of Human Leukocyte Antigen-B27 (HLA-B27) in the Brazilian population, which also identified a higher incidence in the South and Midwest regions [23]. This north-south gradient appears to be related to the genetic characteristics resulting from the process of colonization and miscegenation in the country, with a higher concentration of descendants of Caucasians in the southern regions.

There are no major studies on the incidence of PsA in the global population. The aforementioned meta-analysis [6] shows 8.26 new cases per 100,000 people/year. The incidence has been showing an increasing trend, as has the prevalence [15, 24, 25]. In our study, we found a significant increase in incidence in the years 2019 and 2020. We believe this finding is due not only to an increase in cases but also to an increase in diagnoses. In recent years, the global population has seen an increase in diseases that contribute to the development of PsA, such as obesity and metabolic syndrome. In addition, the greater dissemination of scientific knowledge, more accurate clinical criteria, such as CASPAR classification criteria [26], popularization of diagnostic methods, such as imaging tests, and the improvement of data collection methods, with the wide introduction of digital medical records, may have contributed to our finding.

As our data reflect the population’s access to SUS, it is possible that better access to this system in recent years has also contributed to an increase in diagnoses.

The slightly higher prevalence of the disease in women is similar to that found in Denmark [24] and Taiwan [15] but different from that found in places with geography and population characteristics similar to Brazil, such as Argentina [8] and the United States [25]. We believe that this discrepancy with other American populations is due to the possibility that Brazilian women are more prompt to seek health care than men.

The comorbidities most commonly reported in the literature are obesity, cardiovascular diseases, and hyperuricemia [27], all of which are associated with a higher chance of developing PsA in patients with psoriasis [28,29,30]. Although cardiovascular diseases are associated with most immune-mediated rheumatic diseases [31], their contribution to the increase in mortality has not been well established in the literature [32,33,34]. In this study’s population, the prevalence of systemic arterial hypertension was lower (4.4%) than that observed in other studies (19–35% of the population) [35,36,37]. However, the prevalence of the code for hypertension in our population was close to that in the general population [38].

No comorbidity was often related to PsA in this study [39], such as diabetes, dyslipidemia, or coronary artery disease [40], yet there were hospitalizations for treating coronary artery disease. This may be explained by the fact that, in non-complicated cases of cardiovascular diseases, the treatment is provided by the attending physician in the outpatient setting, not being the main reason for the medical consultation; thus, there is underreporting of comorbidities due to the absence of their code in patients’ records.

The most frequent musculoskeletal comorbidities found in our study were osteoarthritis, shoulder injuries, crystal arthropathies, and osteoporosis. We believe this is due to rheumatologists’ skills in making these diagnoses during the medical visit. Patients with PsA are twice more likely to develop osteoporosis in comparison to the general population [41, 42], which is consistent with the data found in our study. Other conditions reported as comorbidities, such as lower back pain and shoulder injury, are possibly symptoms and secondary changes due to the disease itself, including both the current disease activity and degenerative lesions caused by the disease. This study did not assess the difference between inflammatory or degenerative conditions.

Studies published in 2008 and 2016 [43, 44] show, respectively, a prevalence of 10% and 12% of malignancy in the studied population with PsA, similar to the 14% rate found in our population.

In addition, we believe that the number of hospitalizations we found does not correspond to the actual rate, especially regarding the main cause of hospitalization. It is likely that there was an error in the use of the codes, with the trivialization of the underlying disease as the cause of hospitalization. However, the percentage of hospitalization for treating clinical and cardiovascular complications is similar to that described above [45].

The main limitation of our study is addressing the code used in the medical consultation for diagnosis, both in outpatient follow-up and in hospitalizations, since it is possible that there are discrepancies between the actual reason for the medical consultation and the reported code. Moreover, this study’s data were retrospectively collected and may have been affected by underreported diagnoses. No data regarding mortality in patients with PsA were analyzed.

Despite these limitations, this is the first study using data available in a national system (Outpatient Data System of SUS, SIA/SUS) to analyze PsA care in SUS. More studies, including prospective ones, are needed to evaluate this topic in Brazil since the epidemiology of PsA is extremely important not only for a better understanding of the disease but also for its treatments and the public management of health resources.