Original article
Trends in incidence of adult-onset psoriasis over three decades: A population-based study

https://doi.org/10.1016/j.jaad.2008.10.062Get rights and content

Background

Incidence studies of psoriasis are rare, mainly due to lack of established epidemiological criteria and the variable disease course. The objective of this study is to determine time trends in incidence and survival of psoriasis patients over three decades.

Methods

We identified a population-based incidence cohort of 1633 subjects aged ≥18 years first diagnosed with psoriasis between January 1, 1970 and January 1, 2000. The complete medical records for each potential psoriasis subject were reviewed and diagnosis was validated by either a confirmatory diagnosis in the medical record by a dermatologist or medical record review by a dermatologist. Age- and sex-specific incidence rates were calculated and were age- and sex-adjusted to the 2000 US white population.

Results

The overall age- and sex-adjusted annual incidence of psoriasis was 78.9 per 100,000 (95% confidence interval [CI]: 75.0-82.9). When psoriasis diagnosis was restricted to dermatologist-confirmed subjects, the incidence was 62.3 per 100,000 (95% CI: 58.8-65.8). Incidence of psoriasis increased significantly over time from 50.8 in the period 1970-1974 to reach 100.5 per 100,000 in the 1995-1999 time period (P = .001). Although the overall incidence was higher in males than in females (P = .003), incidence in females was highest in the sixth decade of life (90.7 per 100,000). Survival was similar to that found in the general population (P = .36).

Limitations

The study population was mostly white and limited to adult psoriasis patients.

Conclusion

The annual incidence of psoriasis almost doubled between the 1970s and 2000. The reasons for this increase in incidence are currently unknown, but could include a variety of factors, including a true change in incidence or changes in the diagnosing patterns over time.

Introduction

Psoriasis is a common systemic inflammatory disorder affecting primarily the skin, nails, and occasionally the joints. The prevalence of psoriasis in different populations varies between 0 and 12%,1 with estimates as high as 2.8% in western populations.2, 3 Apart from differences in study populations, the wide variation in prevalence estimates may be due to the remitting relapsing course of psoriasis, wide spectrum in clinical presentation and severity, and, most importantly, lack of standardized classification criteria.4

Studies on the incidence of psoriasis are rare, mostly because of the same limiting factors. Two incidence studies covering different time frames were reported from Olmsted County, Minnesota. Bell et al5 reported an incidence of 60.4 (95% confidence interval [CI]: 49.5-70.3) per 100,000 person-years between 1980 and 1983. Shbeeb et al6 screened all psoriasis cases between 1982 and 1991 and reported an incidence of 107.7 (95% CI: 101.2-114.2) per 100,000. More recently, in a large database study from the United Kingdom, the incidence of psoriasis in the period 1996-1997 was estimated as 140 per 100,000 patient years.7 Intriguingly, the results of these 3 reports from different time periods suggest an increase in the incidence of psoriasis over time. Yet, no studies to date examined trends in incidence of psoriasis.

The objective of this population-based study was to describe time trends in incidence, characteristics, and survival of psoriasis patients in Olmsted County, Minnesota between 1970 and 2000.

Section snippets

Study setting

This population-based retrospective study was carried out in Olmsted County, Minnesota, which has a population of 124,277 according to the 2000 census. We used the resources of the Rochester Epidemiology Project,8 a medical records linkage system containing complete inpatient and outpatient records from all healthcare providers in Olmsted County, including the Mayo Clinic, Olmsted Medical Group, local nursing homes, and the few private practitioners. All medical, surgical, and histological

Results

We identified a total of 3105 potential subjects with diagnostic codes consistent with psoriasis between January 1, 1970 and January 1, 2000. After the complete medical records from all healthcare providers were screened, 1633 (52.6%) psoriasis subjects fulfilled criteria for inclusion in the incidence cohort. Of the 1472 excluded subjects, 64.8% had diagnoses other than psoriasis (eg, parapsoriasis, pityriasis rosea, psoriasiform dermatitis) and 35.2% were prevalent subjects (ie, psoriasis

Discussion

In this population-based study, we describe trends in incidence of psoriasis over time and demonstrate, for the first time, that the incidence of psoriasis increased significantly over the 3 decades between 1970 and 2000. The reasons for this increase in incidence are unknown, but could include a variety of factors, including a true change in incidence or changes in the diagnosing patterns in this population. Our findings also indicate that the age- and sex-specific incidence of psoriasis is in

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    Supported by an unrestricted research grant from Amgen Inc and AR30582 from NIAMS.

    Disclosure: Dr Kremers has received consulting fees, speaking fees, and/or honoraria (less than $10,000) from Amgen. Dr Dann is a former Amgen employee, holds Amgen stock, and has a consultancy agreement with Amgen. Drs Icen, Crowson, McEvoy, and Gabriel declared no conflicts of interest.

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