It’s an interesting question, but one that is difficult to answer definitively because of problems in obtaining accurate data; until recently, more than 80% of countries around the world lacked reliable information on the epidemiology of psoriasis and most estimates were limited to information derived from adult populations in Europe and North America. More recently, however, data from two long-term (30-year) surveys has become available, allowing firmer conclusions regarding psoriasis trends across the globe.
One study published in 2013, was based on five population-based surveys in North Norway - the Tromsø Studies (2-6). Researchers collected sequential data on individuals aged 20-79 years with self-reported psoriasis in at least one of the surveys carried out between 1979 and 2008. In all, there were 69,539 observations from 33,387 unique individuals, born between 1915 and 1977. Trends in psoriasis prevalence were then examined, using a variety of statistical methods1.
Results showed the self-reported lifetime prevalence of psoriasis increased from 4·8% in 1979-1980 to 11·4% in 2007-2008. Individuals in the cohort, were 2.5 times more likely to report psoriasis in 2008 than in 1979. Psoriasis was associated with higher body mass index, lower physical activity during work and leisure time, lower educational level, and smoking.
In this study, however, comprehensive data collection, standardised disease registration and careful follow-up, make interpretation easier and conclusions much more reliable.
A second study from researchers at United Arab Emirates (UAE) University, used the Global Burden of Disease data set to assess the impact of psoriasis in widely geographically distributed populations2. This dataset was constructed by the Institute of Health Metrics at the University of Washington, Seattle, to evaluate the global burden of psoriasis over three- decades in six major geographical regions (Africa, the Americas, Europe, Eastern Mediterranean, Southeast Asia, and the Western Pacific). The UAE researchers used four measures of psoriatic disease-burden, i.e. prevalence, incidence (new diagnosis), disability-adjusted life-years (DALYs), and years lived with disability (YLDs). Age-adjusted values were used to compare rates from 1990 to 2017.
Globally, all four variables increased over the almost three-decades between 1990-2017. Specifically:
- The prevalence of psoriasis increased from 758 cases per 100,000, to 812 cases per 100,000.
- The incidence (new cases) increased from 92.3 cases per 100, 000 to 99.5 per 100,000.
- YLDs, which indicate the burden of suffering increased from 65.2 per 100,000 to 70.
- Finally, DALYs, which combines YLDs with years of life lost to premature deaths and reflects overall suffering, increased from 65.1 per 100,000 to 70, globally.
There were significant differences across regions, with Europe and the Americas (including the USA and Canada), having higher rates for all four measures, when compared with countries in the Western Pacific regions (including China and Australia). The differences observed between regions could be accounted for by a variety of factors, including ascertainment bias – i.e. the fact that some countries have less sophisticated data recording which is a standard feature of most healthcare systems in Western Europe and North America. There may also be significant regional differences in terms of access to medical care. In addition, high-income countries (e.g. USA and UK) tended to have highest rates of psoriasis DALYs, possibly because people in these countries live longer and their countries have a better capacity to handle the costs of psoriasis care.
However, within region differences are more likely to reflect a real increase in both incidence and prevalence, which may be due to a variety of genetic, environmental and lifestyle factors.
Comment
Both studies suggest that over three-decades there has been a real increase in rates of psoriasis, across widely different geographical locations.
In the Norwegian surveys, the trend is dramatic; a two-and a half-fold increase in the prevalence of psoriasis. The UAE study also shows that the global incidence, prevalence, and burden of suffering caused by psoriasis, have been rising over the past three decades. Various factors might explain these trends – e.g. a growing awareness of the disease may be driving earlier diagnosis and treatment. But a variety of environmental and lifestyle factors – including obesity and alcohol consumption - may also be contributing.
Whatever the causes may be, these findings have important implications for healthcare systems across the globe.
References:
1.Kanielsen K, Olsen A O, Wilsgaard T, Furberg A-S. Is the prevalence of psoriasis increasing? A 30-year follow-up of a population-based cohort. Br J Dermatol 2013; 168:1303-10
2.AlQassimi S, AlBrashdi S, Galadari H, Hashim MJ. Global burden of psoriasis - Comparison of regionaland global epidemiology, 1990 to 2017. Int J Dermatol. 2020;59(5):566-571.