Original article
The prevalence of previously diagnosed and undiagnosed psoriasis in US adults: Results from NHANES 2003-2004

https://doi.org/10.1016/j.jaad.2008.09.022Get rights and content

Background

Psoriasis is a predictor of morbidity. It is important to determine the extent to which psoriasis remains undiagnosed.

Objective

To determine the prevalence of psoriasis.

Methods

We conducted a cross-sectional study using the National Health and Nutrition Examination Survey 2003-2004.

Results

The prevalence of diagnosed psoriasis was 3.15% (95% confidence interval [CI], 2.18-4.53), corresponding to 5 million adults. Approximately 17% of these patients have moderate to severe psoriasis based on body surface area report and 25% rate psoriasis a large problem in everyday life. The prevalence of undiagnosed active psoriasis by conservative estimate was 0.4% (95% CI, 0.19-0.82), corresponding to approximately 600,000 US adults, and 2.28% (95% CI, 1.47-3.50) by a broader definition, corresponding to 3.6 million US adults. Undiagnosed patients had a trend toward being more likely to be male, nonwhite, less educated, and unmarried compared with patients who had received a diagnosis.

Limitations

The method for determining the presence of psoriasis had limited ability to detect mild disease and only fair interrater agreement.

Conclusion

More than 5 million adults have been diagnosed with psoriasis. A large number have undiagnosed psoriasis and there are important disparities which may be associated with not receiving medical attention.

Introduction

Psoriasis is a chronic, inflammatory disease of the skin and joints that negatively impacts health-related quality of life. More recent data have also demonstrated that psoriasis, particularly when severe, is associated with metabolic disorders, obesity, excess mortality and may be an independent risk factor for developing atherosclerosis, myocardial infarction, and stroke.1, 2, 3, 4, 5, 6 The treatment paradigm of psoriasis is undergoing a revolution with the recent approval of multiple systemic psoriasis treatments and the development of consensus statements which have broadened recommendations for which patients may qualify for systemic therapy.7, 8 Given these recent advances, it is important to understand how many patients suffer from psoriasis and which patients have disease that has substantial severity and/or impact on quality of life to warrant systemic therapy. Furthermore, since psoriasis is increasingly being recognized to be a predictor of current and future morbidities, it is important to determine the extent to which psoriasis remains undiagnosed in the general population.

Previous estimates of the prevalence of psoriasis in various locations throughout the world have ranged from 0.6% to 4.8%.9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 These studies have varied in source population studied (eg, various ages, general population–based vs clinic-based), definition of prevalence (point vs period vs lifetime), and definition of psoriasis (eg, self report vs physician diagnosed). Two population-based studies in the continental United States of adults have found a prevalence of psoriasis of 2.2%24, 27 and 2.6%9 based on patient report of a physician diagnosis attained by telephone and mail questionnaire, respectively. This approach may underestimate the true prevalence of disease because a significant portion of patients with psoriasis may not seek medical care and therefore be unaware of their diagnosis. The 1971-1974 Health and Nutrition Examination Survey of persons 1-74 years of age found a point prevalence of psoriasis of 1.4% based on physician examination.10 This study did not evaluate whether a patient had ever had psoriasis in the past and therefore may underestimate the prevalence of psoriasis as the disease may be in remission because of treatment, seasonal changes, or natural history.9

A more comprehensive method of assessing the prevalence of psoriasis is needed in order to capture psoriasis patients who are aware of their diagnosis as well as those who may remain undiagnosed. To further investigate the prevalence of psoriasis in the general US population, we examined data from the National Health and Nutrition Examination Survey (NHANES) (2003-2004), which is unique in that it contains both information ascertained by patient report and physician examination and therefore can be used to determine the prevalence of psoriasis in patients who are aware of their diagnosis as well as the prevalence of psoriasis in patients with active yet previously undiagnosed psoriasis.

Section snippets

Study design

We investigated the prevalence of psoriasis by analyzing data from the NHANES in the United States from 2003 through 2004. The study was approved by the National Center for Health Statistics institutional review board and all subjects gave informed consent. NHANES is an ongoing population-based, cross-sectional study which is designed to assess the health and nutritional status of people living in the United States. It is unique in that it combines interviews and physical examinations, and the

Results

The dermatologic interview and examination were only administered to subjects aged 20-59 years and represent a subset of the total NHANES data which includes all ages. An unweighted sample size of 4,163 people aged 20-59 years were screened, 3140 of whom participated in questionnaire-based interviews. A total of 2984 of the interviewed subjects had nonmissing psoriasis questionnaire data and this was the cohort used to calculate prevalence estimates of psoriasis. Data from dermatologist review

Discussion

The unique design of the NHANES 2003-2004 in which the prevalence of psoriasis was measured by both patient self-report of a prior healthcare provider diagnosis as well as by review of clinical photographs provides important confirmation of previous epidemiological studies as well as novel findings. First, the prevalence of self report of a healthcare provider diagnosis of psoriasis is statistically similar to previous estimates in the US adult population using comparable methods.9, 24 Second,

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    Supported in part by a National Research Service Award from the National Institute of Health (to S.K.K.) and a grant K23AR051125 from the National Institutes of Health/National Institute of Arthritis, Musculoskeletal, and Skin Diseases (to J.M.G.).

    Conflicts of interest: None declared.

    Reprints not available from the authors.

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