Systematic review examining changes over time and variation in the incidence and prevalence of psoriasis by age and gender

Background There is a lack of any overview of changes over time and variation in the epidemiology of psoriasis with age and between genders. Objectives To perform a systematic review of published population-based studies on variations in psoriasis incidence and prevalence with age and between genders, and to explore trends in psoriasis epidemiology over time. Methods Eleven electronic and regional databases were searched from their inception dates to October 2019. No language restrictions were applied. Studies were eligible if they reported on changes in psoriasis incidence and/or prevalence over time and/or by age group and gender. Results In total 308 papers were critically appraised, from which 90 studies from 22 countries were included. Incidence data confirmed a clear bimodal age pattern in psoriasis onset, with the first and second peaks at around 30-39 and 60-69 years of age, respectively, and evidence suggesting that it presents slightly earlier in women than in men. Prevalence data showed an increasing trend with age until around 60 or 70 years, after which it decreases. Although there was lack of agreement on specific gender differences in psoriasis incidence and prevalence, a slight male predominance was reported in several studies. Studies worldwide suggested a stable or slightly decreasing trend in psoriasis incidence, while an increasing trend in psoriasis prevalence has been consistently reported. One particular challenge faced was the vastly different methodologies used in the included studies, which contributed to some of the heterogeneity of the results. Conclusions Studies on changes over time in the occurrence of psoriasis have contributed to a greater appreciation of the increasing burden of the disease. However, further research is required to determine the reasons driving the increase in psoriasis prevalence over time.