Epidemiological characteristics of psoriatic arthritis.

Psoriatic arthritis (PsA) is a specific form of inflammatory arthritis associated with skin psoriasis. PsA makes part of a heterogeneous group of arthritides called the spondyloarthropathies. Several studies regarding the prevalence and incidence of PsA have been published during the last decades, showing a considerable variation of the disease occurrence among different populations. The purpose of this review is to discuss recent observations of epidemiological features for PsA patients. Thus, the literature was reviewed until May 2018 for studies regarding PsA epidemiology, classification criteria and risk factors for PsA development. Systematic reviews based on the international bibliography, are reporting the prevalence of the disease from 1/100.000 inhabitants in Japan to as high as 420/100.000 inhabitants in Italy. The annual incidence also varies, ranging from 1 to 23/100.000 inhabitants, while the average incidence rate is 6.5 cases/100.000 inhabitants. The random effect pooled PsA prevalence and incidence rates are 133/100.000 and 83/100.000 subjects respectively. Thus, a large heterogeneity between studies is observed. This variability could be explained by a number of factors such as the use of multiple and different classification criteria in the studies. Geographical variations are also observed regarding disease occurrence. Differences were found not only between different continents, but also within the same geographic regions. This could be explained by the different genetic background especially the distribution of the human leucocyte antigens. In addition, other factors such as environmental (infections, climate, sun exposure), dietary habits (fish oil consumption, Mediterranean diet) or life style habits (obesity, smoking), could explain the geographic variability in the prevalence estimates. The implementation of unanimous classification criteria and the conformation by the scientific community could lead to a better understanding of the disease epidemiology.