Prevalence and incidence of palmoplantar pustulosis in Sweden: a population‐based register study

Summary Background Palmoplantar pustulosis (PPP) is a chronic relapsing skin condition characterized by sterile pustules on the palm and soles. Population‐based estimates of PPP incidence and prevalence are limited. Objectives To estimate the prevalence and incidence of PPP in the Swedish general population and to estimate the prevalence of psoriasis vulgaris among the population with PPP. Methods The Swedish National Patient Register was used, covering all inpatient and outpatient nonprimary care for the Swedish population. We identified cases (2004–2015) with one International Classification of Diseases 10th Revision diagnostic code (base case) for PPP. The point prevalence estimates at the end of this period (31 December 2015) were obtained by linkage to the Swedish Total Population Register. In sensitivity analyses, we used alternative case definitions: (i) requiring two visits and (ii) requiring two visits, one of which was within dermatology or internal medicine. Results The base case prevalence of PPP was estimated to be 147 per 100 000 (women 227, men 68) and the annual prevalence was estimated to 26 per 100 000 in 2015. Among the population of people with PPP, 17% were registered with a diagnostic code for psoriasis vulgaris. The incidence of PPP in 2015 was estimated to be 12·7 per 100 000 (women 18·7, men 6·6). The criteria used had an impact on the prevalence and incidence estimates: strict case 1 gave an overall prevalence of 72 per 100 000 and an incidence of 5·4 per 100 000. Conclusions The results indicate that the population‐based prevalence of PPP may be larger than previously estimated. However, the estimates were sensitive to the employed PPP case criteria. The findings enhance demands for studies using validated diagnostic algorithms potentially also including data from primary care. What is already known about this topic? There are few published estimates of the prevalence and incidence of palmoplantar pustulosis (PPP). The previous studies are mainly based on short observation periods and often lack coverage of the general population. Previous studies, with use of different case definitions and prevalence measures, show large variations (range from 50 to 120 per 100 000) in the prevalence estimates of PPP. What does this study add? We found a population‐based point prevalence on 31 December 2015 of 147 per 100 000, an annual prevalence of 26 per 100 000, and an incidence estimate of 12·7 cases of PPP per 100 000 in 2015. The populati