Psoriasis, Psoriatic Arthritis Linked With Age, Earlier Birth Cohorts

Despite incidence of psoriasis decreasing, older populations in Taiwan have a higher risk of developing psoriasis and psoriatic arthritis, according to a recent study.

Psoriasis and psoriatic arthritis (PsA) are associated with older age and early birth cohorts, meaning elderly individuals may be at a higher risk of developing these conditions, according to a study recently published in the Journal of Clinical Medicine.

Most research conducted on psoriasis and PsA comes from Western countries and have rarely included the effects of age, period, and birth cohort on the prevalence or incidence of psoriasis, which is less common in Asian countries. Part of this reason is due to genetics; the authors said that the gene most strongly linked with susceptibility to the disease—human leukocyte antigen (HLA)-Cw6 locus—is expressed at lower levels in Taiwanese populations compared with White populations.

However, the difference may also depend on lifestyle factors that may be more common among certain groups born in a particular era, or the development of health advances. To that end, researchers sought to examine trends in psoriasis from 2002 to 2016 in Taiwan using an age-period-cohort (APC) model to distinguish the independent effects of these factors on the temporal trends.

They used data from the National Health Insurance Research Database and identified 112,865 psoriasis incident cases, for an average incident rate of 34.21 per 100,000 persons. The incidence of psoriasis significantly decreased from 43.33 to 23.14 per 100,000 persons from 2002 to 2016.

However, the incidence of PsA significantly increased from 3.57 to 5.22 per 100,000 persons over the same time period, and hit a peak of 6.76 per 100,000 persons in 2014.

Though incidence of psoriasis had decreased, psoriasis prevalence increased with an annual change of 6.8% (P < .001). The prevalence of PsA also increased with an annual change of 11% (P < .001).

Given that previous research shows severe psoriasis to be associated with a higher risk of developing PsA, the authors suggest that the increasing incidence of PsA was associated with the increasing prevalence of psoriasis. Despite the decreasing trend for the incidence of psoriasis, this may explain the rising incidence rate of PsA.

The APC analysis demonstrated that the net age effect on the incidence of psoriasis and PsA increased with increasing age. The oldest birth cohort had the highest psoriasis incidence rate, 17-fold higher than the youngest birth cohort.

The net period effect exhibited a decreasing trend for psoriasis but an increasing trend for PsA. The rate ratio for incidence showed a decrease of approximately 25% for psoriasis, whereas it showed a 1.7-fold increase for PsA during the observation period.

The net cohort effect on psoriasis and PsA incidence continuously decreased from 1937, according to the study. The rate ratio for the incidence of psoriasis and PsA showed 43.4% and 72.1% decreases, respectively, from the earliest to the most recent birth cohorts.

The authors note that this may be due to later cohorts (ie, younger individuals) having good education about health issues and increased awareness of healthy lifestyles, compared with earlier birth cohorts, who may have had different health habits more common to an older generation.

Overall, the results from the statistical analysis revealed a significant decreasing trend in the incidence of psoriasis and a significant increasing trend in the incidence of PsA. Although the incidence rates showed opposite trends, the incidence of both conditions remained high in the older population.

The authors suggest that the increase in either or both psoriasis and PsA prevalence may be related to a better awareness of the disease, a reduction in mortality, or an actual increase in prevalence.

Additionally, they note that the decreasing and increasing trends in psoriasis incidence and prevalence, respectively, suggest a decline in psoriasis-related mortality; longitudinal studies are warranted to examine this hypothesis, they said.

The researchers hope their findings can support better understanding of psoriasis and PsA, as well as help with the allocation of medical care and improvement of health care policy. They recommend conducting comprehensive projects on health-promoting behaviors and effective screening strategies, especially for middle-aged and older individuals. To address the risks of PsA and delayed diagnosis, they also encouraged collaborations between dermatologists and rheumatologists.

The study had some limitations. The APC model produces an estimate, so causality could not be determined for the observed associations.

Additionally, the inclusion of only patients seeking care at a department of dermatology and rheumatology with 3 consecutive visits could have resulted in an underestimation of the incidence and prevalence of both psoriasis and PsA.


Chen YT, Wu CY, Li YL, Chen LY, Chiou HY. Time trends in psoriasis and PsA incidence from 2002 to 2016 in Taiwan: an age-period-cohort analysis. J. Clin. Med. 2022;11(13):3744.

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