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.
Background Electronic claims and medical record databases are increasingly used for observational studies of psoriasis. The purpose of this study was to assess the validity of psoriasis diagnostic ...codes in an electronic database. Methods This study was performed in a population-based setting in Olmsted County, Minnesota, where all diagnoses and procedures from all health care providers in a large community are indexed and recorded in an electronic database. The database was searched for patients aged 18 years or older with diagnostic codes consistent with psoriasis for the time period January 1, 1976, to January 1, 2000. The complete medical records of all patients were reviewed manually for validation of psoriasis diagnoses. Results We reviewed the complete medical records of 2556 patients with at least one diagnostic code consistent with psoriasis. Based on medical record review, 1458 (57.0%) patients were confirmed to have psoriasis, of which the majority (81%) received confirmation by a dermatologist. The most commonly used diagnostic codes for psoriasis were International Classification of Diseases, Ninth Revision 696.1 (psoriasis, not otherwise specified) with a positive predictive value of 68.7% (95% confidence interval: 66.5%, 70.9%). Increasing frequency of codes in a given time window was associated with positive predictive values. However, positive predictive value for only one code in a 5-year time window was still as high as 60% (95% confidence interval: 57%, 63%). Limitations Differences between individual electronic medical record databases may limit the ability to form a general conclusion from these findings. The remitting, relapsing course of psoriasis and the heterogeneity in clinical presentation create challenges in case ascertainment. Conclusion Electronic identification of patients with psoriasis by diagnostic codes alone may lead to misclassification in database studies.
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