Objective. To determine the incidence and disease-specific predictors of clinically recognized psoriatic arthritis (PsA) in patients with psoriasis. Methods. We identified an incidence cohort of psoriasis subjects age >18 years diagnosed between January 1, 1970 and December 31, 1999 in a population-based setting. Psoriasis diagnoses were validated by confirmatory diagnosis in the medical record. Incident and clinically recognized PsA subjects were classified according to the Classification of Psoriatic Arthritis (CASPAR) criteria. Cox proportional hazards models were used to identify predictors of PsA within the psoriasis cohort. Results. The psoriasis incidence cohort comprised 1,633 subjects. Of these, 40 were diagnosed with PsA concurrently with psoriasis and were excluded from analysis. The remaining 1,593 psoriasis subjects had a mean age of 43 years and 50% were men. Over 20,936 person-years of followup, 57 subjects were clinically recognized with new-onset PsA, with a cumulative incidence of 1.7% (95% confidence interval [95% CI] 1.0 -2.3%), 3.1% (95% CI 2.2-4.1%), and 5.1% (95% CI 3.7-6.6%) at 5, 10, and 20 years following psoriasis incidence, respectively. Psoriasis features associated with higher risk of PsA were scalp lesions (hazard ratio [HR] 3.89, 95% CI 2.18 -6.94), nail dystrophy (HR 2.93, 95% CI 1.68 -5.12), and intergluteal/perianal lesions (HR 2.35, 95% CI 1.32-4.19). Calendar year was not associated with risk of PsA (P ‫؍‬ 0.15), indicating that the likelihood of PsA in psoriasis subjects did not change over time. Conclusion. In this population-based study, <10% of patients with psoriasis developed clinically recognized PsA during a 30-year period. Psoriasis features associated with a higher likelihood of PsA were nail dystrophy, scalp lesions, and intergluteal/perianal psoriasis.

Background Although psoriasis is considered to have a “dual peak” in age of onset, currently no studies exist regarding the incidence of psoriasis in children. Objective The objective of this study is to determine the incidence of psoriasis in childhood. Methods A population-based incidence cohort of children aged <18 years first diagnosed with psoriasis between January 1, 1970 and December 31,1999 was assembled. The complete medical record of each child was reviewed and psoriasis diagnosis was validated by 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 2000 U.S. white population. Results The overall age and sex adjusted annual incidence of pediatric psoriasis was 40.8 per 100,000 (95% confidence interval 1: 36.6, 45.1). When psoriasis diagnosis was restricted to dermatologist confirmed subjects in the medical record, the incidence was 33.2 per 100,000 (95% CI: 29.3, 37.0). Incidence of psoriasis in children increased significantly over time from 29.6 per 100,000 in 1970 to 1974 to 62.7 per 100,000 in 1995-1999 (p<0.001). Chronic plaque psoriasis was the most common type (73.7%), and the most commonly involved sites were the extremities (59.9%) and the scalp (46.8%). Limitations The population studied was a mostly Caucasian population in the upper Midwest. Conclusion The incidence of pediatric psoriasis increases with increasing age. There is no apparent “dual-peak” in incidence. The incidence of pediatric psoriasis increased in recent years in both boys and girls.

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.

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