Incidence and prevalence of psoriatic arthritis: a systematic review.

OBJECTIVE: Descriptive epidemiological studies of psoriatic arthritis (PsA) in the general population were very limited until the year 2000. Recently, several incidence and prevalence studies of PsA have been reported, suggesting a considerable variation of the disease frequency among different populations. We present a systematic review of incidence and prevalence studies of PsA published after 1987 until December 2006, in order to evaluate and compare their methodology and to summarize their results, and to investigate the possible geographic variations of occurrence of PsA.

METHODS: We conducted a MedLine search including all articles published on PsA incidence and prevalence in the general adult population until December 2006. From each study identified, we extracted the country, year of publication, type of study, criteria of case identification, and incidence or prevalence rates. Methodological criteria for quality included the type of study (prospective or retrospective for incidence studies and retrospective or cross-sectional for prevalence studies), the type of incidence and prevalence rates (crude or adjusted), the criteria of case definition, and the description of the characteristics of the population studied.

RESULTS: A total of 13 studies were identified from the literature search meeting our inclusion criteria. There is a wide variation of annual incidence of PsA (median 6.4, range 0.1-23.1 cases per 105 inhabitants). One incidence study used European Spondylarthropathy Study Group (ESSG) criteria for case definition, while the other studies were based on a coexistence of psoriasis and arthritis in several ways. Three prevalence studies used ESSG criteria for case identification, while the other studies were based on a coexistence of psoriasis and arthritis in several ways. The prevalence estimates vary from 1 case per 105 population in a Japanese study to 420 cases per 105 population in an Italian study (median 180).

CONCLUSION: The occurrence and epidemiological profile of PsA are likely to present important variations among countries and areas of the world. However, several methodological issues and mainly the absence of validated or consensual criteria for case identification and classification of the disease put important limitations on the interpretation of epidemiological data. The establishment of standardized criteria for the diagnosis and classification of PsA cases is necessary for further, valid investigation of the disease epidemiology.