Trends in incidence of adult-onset psoriasis over three decades: a population-based study.

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 > or = 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.