Epidemiology of psoriatic arthritis

Epidemiology aims to investigate both the distribution of rheumatic diseases and the risk factors for their development. Epidemiologic studies on psoriatic arthritis (PsA) have long been hampered by the absence of widely accepted classification criteria. As a consequence, different studies have used different sets of criteria ranging from the European Spondyloarthropathy Study Group (ESSG) (1) and Wright & Moll (2) to ad hoc criteria, all of which are prone to some degree to misclassifying patients. In particular, the ESSG criteria have a relatively low sensitivity and specificity (1), while the Moll and Wright criteria tend to be overinclusive (2). The recent development of the CASPAR (ClASsification criteria for Psoriatic ARthritis) criteria has provided a more robust framework for conducting epidemiological studies in PsA given the high sensitivity (0.91) and specificity (0.99) of these criteria (3). In addition, the CASPAR criteria have been validated quite extensively and have been shown to perform well, at least in established PsA (3, 4). However, only a small minority of epidemiological studies in PsA have used the CASPAR criteria. Other discrepancies between published studies include different study settings, designs, and ascertainment methods. These differences render difficult to compare the results from different studies, which have found widely varying estimates of incidence (from 3,02 to 23,1 cases per 100,000 people) and prevalence (from 49,1 to 420 cases per 100,000 people) (5-30). On the other hand, some differences may be genuine and reflect genetic or environmental factors. For instance, the frequency of PsA has consistently been reported to be quite low (up to 1/100,000) in Japan (7). Most incidence studies available are retrospective in design and have used either medical records or else diagnostic or insurance codes to determine the incidence of PsA in general or Hospital populations (5-15) (Table I). Prospective studies have usually yielded higher incidence rates than retrospective studies. Data from a populationbased incidence cohort suggests a rise of the incidence of PsA over the last three decades (12). However, it is debatable whether this rising incidence is genuine or simply reflects a greater awareness of physicians. As for prevalence studies, the majority Corresponding author: Dr. Carlo Salvarani Head of the Department of Rheumatology Arcispedale Santa Maria Nuova Viale Risorgimento, 80 42123 Reggio Emilia, Italy E-mail: Salvarani.carlo@asmn.re.it SUMMARY Epidemiological studies on psoriatic arthritis have long been hampered by the absence of widely accepted classification criteria. The development of the CASPAR (ClASsification criteria for Psoriatic ARthritis) criteria has recently provided the framework for conducting epidemiological studies in psoriatic arthritis using uniform recruitment criteria. However, so far, only a minority of studies have adopted such criteria. In addition to the lack of shared classification criteria, differences in study settings, designs, and ascertainment methods have contributed to yield substantial disparities in the estimates of the incidence (from 3,02 to 23,1 cases per 100,000 people) and prevalence (from 49,1 to 420 cases per 100,000 people) of psoriatic arthritis around the globe. Overall, the available data suggests that the prevalence of psoriasis in the general population is approximately 2-3%, with about a third of patients with psoriasis having arthritis. Therefore, psoriatic arthritis may affect 0,31,0% of the population, a frequency not dissimilar from that of rheumatoid arthritis. Future epidemiological studies should be carried out in larger numbers of patients diagnosed using consistent criteria.

review Reumatismo, 2012; 64 (2): 66-70   Epidemiology of psoriatic arthritis M. Catanoso, N. Pipitone, C. Salvarani Unità Operativa di Reumatologia, Dipartimentodi Medicina Interna, Azienda Ospedaliera ASMN, Istituto di Ricovero e Cura a Carattere Scientifico, Reggio Emilia, Italy E pidemiology aims to investigate both the distribution of rheumatic diseases and the risk factors for their development.Epidemiologic studies on psoriatic arthritis (PsA) have long been hampered by the absence of widely accepted classification criteria.As a consequence, different studies have used different sets of criteria ranging from the European Spondyloarthropathy Study Group (ESSG) (1) and Wright & Moll (2) to ad hoc criteria, all of which are prone to some degree to misclassifying patients.In particular, the ESSG criteria have a relatively low sensitivity and specificity (1), while the Moll and Wright criteria tend to be overinclusive (2).The recent development of the CASPAR (ClASsification criteria for Psoriatic ARthritis) criteria has provided a more robust framework for conducting epidemiological studies in PsA given the high sensitivity (0.91) and specificity (0.99) of these criteria (3).In addition, the CASPAR criteria have been validated quite extensively and have been shown to perform well, at least in established PsA (3,4).However, only a small minority of epidemiological studies in PsA have used the CASPAR criteria.
Other discrepancies between published studies include different study settings, designs, and ascertainment methods.These differences render difficult to compare the results from different studies, which have found widely varying estimates of incidence (from 3,02 to 23,1 cases per 100,000 people) and prevalence (from 49,1 to 420 cases per 100,000 people) .On the other hand, some differences may be genuine and reflect genetic or environmental factors.For instance, the frequency of PsA has consistently been reported to be quite low (up to 1/100,000) in Japan (7).Most incidence studies available are retrospective in design and have used either medical records or else diagnostic or insurance codes to determine the incidence of PsA in general or Hospital populations (5-15) (Table I).Prospective studies have usually yielded higher incidence rates than retrospective studies.Data from a populationbased incidence cohort suggests a rise of the incidence of PsA over the last three decades (12).However, it is debatable whether this rising incidence is genuine or simply reflects a greater awareness of physicians.As for prevalence studies, the majority review Epidemiology of psoriatic arthritis is cross-sectional and population-based, while a minority is retrospective and based on medical records.A few studies have examined the prevalence of PsA in the population of people with psoriasis.Recent cross-sectional surveys tend to yield higher prevalence estimates than retrospective prevalence studies.(5-30) (Table II).Many studies have reported that the onset of psoriasis typically precedes the development of arthritis.Approximately 85% of patients develop psoriasis prior to arthritis, while in 5-10% of patients both conditions develop simultaneously, and in 5-10% arthritis precedes psoriasis.There is some evidence suggesting that the severity of psoriasis is associated with an increased risk, although not greater severity of arthritis (31).The prevalence of psoriasis in the general population is circa 2-3%, with about a third of patients with psoriasis having arthritis.Genetic factors have been linked to both psoriasis and PsA.In particular, HLA-B13, B16 and its splits HLA-B38 and HLA- B39, B17, and Cw6 have been associated with psoriasis, while HLA-B7 and B27 have been associated with PsA (32).Some environmental factors, including HIV infection, trauma, and psychological stress appear to increase susceptibility to developing PsA.In addition, a number of clinical features including nail dystrophy, scalp lesions, and intergluteal/perianal psoriasis have been mapped to a higher likelihood of PsA (16).Patients with PsA have been found to have increased risk factors for cardiovascular disease including hypertension, dyslipidemia and insulin resistance (33).Other studies have shown subclinical atherosclerosis and an atherogenic lipid profile (34)(35)(36).There is an increased prevalence of the metabolic syndrome in patients with psoriasis, particularly in those with moderate to severe skin disease (37).
Studies that have investigated mortality in PsA have thus far produced conflicting results, with a community-based study showing no increase in mortality (6,12) while the analysis of a hospital-based cohort estimated a combined Standardized Mortality Ratio (SMR) for both men and women to be 1.62 (38).Recently, a single-center study suggested that mortality rates in the PsA cohort were not significantly different from those of the UK general population (39).
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Table I -
incidence studies of PsA.

Table II -
Prevalence studies of PsA.