The prevalence of previously diagnosed and
`undiagnosed psoriasis in US adults: Results from
`NHANES 2003-2004
`
`Shanu Kohli Kurd, MHS,a,b and Joel M. Gelfand, MD, MSCEa,b
`Philadelphia, Pennsylvania
`
`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. ( J Am Acad Dermatol 2008;60:218-24.)
`
`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 demon-
`strated that psoriasis, particularly when severe, is
`
`From the Department of Dermatologya and Center for Clinical
`Epidemiology and Biostatistics,b University of Pennsylvania
`School of Medicine.
`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.
`Accepted for publication September 17, 2008.
`Reprints not available from the authors.
`Correspondence to: Joel M. Gelfand, MD, MSCE, University of
`Pennsylvania, Department of Dermatology, 3600 Spruce St, 2
`Maloney Building Suite 2M47, Philadelphia, PA 19104. E-mail:
`Joel.Gelfand@uphs.upenn.edu.
`Published online November 21, 2008.
`0190-9622/$36.00
`ª 2008 by the American Academy of Dermatology, Inc.
`doi:10.1016/j.jaad.2008.09.022
`
`218
`
`Abbreviations used:
`
`body surface area
`BSA:
`confidence interval
`CI:
`mobile examination center
`MEC:
`NHANES: National Health and Nutrition
`Examination Survey
`odds ratio
`
`OR:
`
`associated with metabolic disorders, obesity, excess
`mortality and may be an independent risk factor for
`developing atherosclerosis, myocardial
`infarction,
`and stroke.1-6 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 pa-
`tients have disease that has substantial severity
`and/or impact on quality of life to warrant systemic
`
`Medac Exhibit 2043
`Koios Pharmaceuticals v. Medac
`IPR2016-01370
`Page 00001
`
`

`

`J AM ACAD DERMATOL
`VOLUME 60, NUMBER 2
`
`Kurd and Gelfand 219
`
`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%.9-26 These studies have
`varied in source population studied (eg, various
`ages, general populationebased vs clinic-based),
`definition of prevalence (point vs period vs lifetime),
`and definition of psoriasis (eg, self report vs physi-
`cian 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 underesti-
`mate 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.
`
`METHODS
`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
`
`the
`physical examinations, and the purpose of
`NHANES initiative is to determine the prevalence of
`major diseases and risk factors for diseases in the
`United States. NHANES data are collected in 2-year
`cycles using a continuous stratified sampling tech-
`nique. The first step is for participants to complete an
`interviewer-administered questionnaire. Physical ex-
`aminations are conducted within 1 to 2 weeks of the
`in-home interview in specially designed and equip-
`ped mobile examination centers (MECs). The survey
`team consists of a physician, medical and health
`technicians, and dietary and health interviewers who
`are extensively trained. The prevalence of psoriasis
`was determined by patient
`interview as well as
`examination of standardized clinical photographs
`by two dermatologists.
`
`Study population
`This study uses a subset of the NHANES survey
`from 2003-2004 which is representative of the non-
`institutionalized US civilian population aged 20-59
`years, which was selected using a complex, multi-
`stage, stratified sampling design. African Americans,
`Mexican Americans, and low-income white Americans
`have been oversampled to increase the accuracy
`and precision of estimates of health status indicators
`for these population subgroups. The sample weights
`for NHANES 2003-2004 reflect the unequal prob-
`abilities of selection, nonresponse adjustments and
`adjustments to independent population controls, and
`sampling adjustments are made during statistical
`analysis.
`
`Definition of psoriasis
`The prevalence of psoriasis was defined by two
`methods. The prevalence of previously diagnosed
`psoriasis was determined by interviewer-assisted
`questionnaire. A response of ‘‘yes’’ when asked
`‘‘Have you ever been told by a health care provider
`that you had psoriasis?’’ was classified in our study as
`having psoriasis. This self-report method of ascer-
`taining the prevalence of psoriasis has been well
`accepted in numerous epidemiological studies of
`psoriasis.9,15,19,24,27
`The presence of psoriasis was also determined by
`review of standardized clinical photographs by two
`dermatologists. The data collection method con-
`sisted of taking standardized images of potentially
`affected areas of the skin during the MEC examina-
`tion using a digital camera. Sites included the back,
`lower extremities, hands, and arms as follows: one
`image of the back that includes the elbows; one
`image of the left upper inner arm; one image of the
`dorsal surface of both hands combined with an
`image of the front lower legs; and one image of the
`
`Page 00002
`
`

`

`220 Kurd and Gelfand
`
`J AM ACAD DERMATOL
`FEBRUARY 2009
`
`palm of both hands combined with an image of
`the back and lower legs. Prior to concluding the
`examination, images were checked for quality. The
`images were then transferred to a digital video disc
`and given to two independent dermatologists for
`analysis.
`A diagnosis of psoriasis by both dermatologists in
`a patient who reported no history of diagnosis of
`psoriasis by questionnaire was used as our conser-
`vative definition of ‘‘undiagnosed active’’ psoriasis. A
`diagnosis by at least one dermatologist in a patient
`who reported no history of diagnosis of psoriasis by
`questionnaire was used as our less conservative
`definition of ‘‘undiagnosed active’’ psoriasis.
`
`Definition of covariates
`Those patients who reported a previous diagnosis
`of psoriasis by questionnaire were asked additional
`questions regarding the extent of their psoriasis as
`well as the impact that psoriasis has on their daily
`lives. Patients were asked, ‘‘Do you currently have
`little or no psoriasis, only a few patches that could be
`covered by one or two palms of your hand, scattered
`patches that could be covered between 3 and 10
`palms of your hand, or extensive psoriasis covering
`large areas of the body that would require more than
`10 palms of your hand?’’ By convention, the palm of
`the hand is estimated to be approximately 1% body
`surface area (BSA) and therefore we present these
`categories as little/no psoriasis, 1%-2% BSA, 3%-10%
`BSA, and [10% BSA, respectively.28 For additional
`and logistic regression analyses, psoriasis severity
`categories were dichotomized into mild (\3%) and
`moderate to severe ( $ 3%). Patients were asked to
`answer the question ‘‘On a scale of 1 to 10 how much
`of a problem has your psoriasis been in your every-
`day life where 1 means no problem at all and 10
`means a very large problem.’’ Ordinal categories
`were created for additional analyses in a manner
`identical to previously published work (1-3: no or
`little impact, 4-7: a problem, 8-10: a large problem).24
`Additional covariate information for all patients
`such as age, gender, race, education, income, health
`insurance and marital status were determined by
`questionnaire. Education was dichotomized into
`greater than high school education or not. Income
`was dichotomized into less than or equal to a median
`income level of $35,000-$44,999 or greater and
`marital status was dichotomized into married or not
`married. In descriptive statistics, the prevalence of
`race was reported based on questionnaire categories
`(Caucasian, black, Hispanic, other) but for logistic
`regression was dichotomized into white or non-
`white.
`
`Other variables of interest such as frequency of
`physician visits, current smoking, alcohol use, de-
`pression and anxiety screening were not used be-
`cause of a high proportion of missing data. To
`maintain quality analyses, only covariates for which
`data were recorded in at least 90% of patients were
`included.
`
`Statistical methods
`All statistical analyses were performed using sur-
`vey commands of STATA to incorporate sample
`weights and adjust for clusters and strata of the
`complex sample design (Version 10, STATA Corp,
`College Station, Tex). The prevalence of psoriasis
`was determined by responses to the dermatological
`questionnaire as well as dermatological clinical
`evaluation. Prevalence and covariate data were
`reported as percentages with 95% confidence inter-
`vals using the survey tabulate command in STATA.
`Odds ratios (ORs) with 95% confidence intervals
`were calculated using survey logistic regression for
`both unadjusted and adjusted (for age and gender)
`analyses. Quality of life data were analyzed using
`logistic regression and linear regression. Agreement
`about the presence of psoriasis on the clinical pho-
`tographs was assessed via the kappa statistic. All
`P values reported are two sided.
`
`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 esti-
`mates of psoriasis. Data from dermatologist review of
`clinical photographs were available for 90% of
`patients in this cohort. The raw data include 73
`patients with psoriasis as determined by self-report
`of a healthcare provider diagnosis on questionnaire.
`Upon examination of standardized photographs, 84
`patients were determined to have active psoriasis by
`at least one dermatologist, 66 of whom by self-report
`had never received a prior diagnosis of psoriasis by a
`healthcare provider. Among the 73 patients who
`reported a prior healthcare provider diagnosis of
`psoriasis, the presence of psoriasis, based on review
`of the standardized clinical photographs, could only
`be confirmed by at least one of two dermatologists in
`18 patients. Confirmation of active psoriasis was
`strongly dependent upon patient self report of skin
`severity. For example, the odds of one or both
`
`Page 00003
`
`

`

`J AM ACAD DERMATOL
`VOLUME 60, NUMBER 2
`
`Kurd and Gelfand 221
`
`Table I. Summary statistics of psoriasis patients, 20-59 years of age, in the US population*
`
`Psoriasis
`
`History of healthcare
`provider diagnosis
`
`Undiagnosed active
`psoriasis: Conservative
`y
`estimate
`
`Undiagnosed active
`psoriasis: Less
`conservative estimate
`
`z
`
`No psoriasis
`
`NA
`
`3.15 (2.18-4.53)
`1.62% (1.02-2.55)
`1.53% (0.97-2.40)
`48.61% (35.54-61.86)
`41.11 (38.80-43.42)
`
`0.40% (0.19-0.82)
`
`82.31% (25.62-98.43)
`44.06 (34.58-53.54)
`
`49.03% (47.69-50.36)
`38.91 (38.10-39.72)
`
`68.79%
`12.16
`13.29
`5.76
`43.91 (39.49-48.43)
`
`81.61%
`7.96
`6.53
`3.9
`37.37 (28.24-47.49)
`
`79.94
`12.19
`7.87
`0
`26.89 (4.78-72.94)
`
`2.28% (1.47-3.50)
`0.48% (0.22-1.03)
`1.8% (1.15-2.8)
`79.1% (63.99-88.96)
`41.69 (38.74-44.64)
`
`70.01
`16.76
`4.44
`8.79
`51.63 (36.83-66.16)
`
`42.59 (40.38-44.83)
`
`29.51 (19.58-41.86)
`
`57.17 (25.50-83.89)
`
`56.85 (45.58-67.45)
`
`43.86 (40.45-47.32)
`22.59 (20.44-24.89)
`
`31.79 (23.01-42.09)
`16.5 (9.19-26.83)
`
`37.97 (11.62-74.03)
`0
`
`47.10 (29.19-65.79)
`27.16 (14.63-44.79)
`
`Psoriasis prevalence, %
`(95% CI)
`Overall
`Women
`Men
`Gender, % male (95% CI)
`Mean age (95% CI)
`Race, %
`White
`Black
`Hispanic
`Other
`Income # median,§ %
`(95% CI)
`No advanced (post-high
`school) education, %
`(95% CI)
`Not married, % (95% CI)
`No health insurance, %
`(95% CI)
`
`CI, Confidence interval.
`*Psoriasis patients with a history of healthcare provider diagnosis and patients with undiagnosed active psoriasis are compared with
`patients without psoriasis.
`y
`The conservative estimate of undiagnosed active psoriasis is determined by agreement of psoriasis by both dermatologists upon review of
`standardized photographs in a patient who reported no previous diagnosis of psoriasis by a healthcare provider.
`z
`Undiagnosed active psoriasis by less conservative estimate is determined by at least one dermatologist upon review of standardized
`photographs in a patient who reported no previous diagnosis of psoriasis by a healthcare provider.
`§Median income is $35,000 to $44,999.
`
`evaluators confirming psoriasis was 11.71 (95% CI,
`4.03-33.98; P \ .001) and 9.71 (95% CI, 1.77-53.34;
`P = .01), respectively, for patients with self reported
`BSA $ 3% compared with patients with no to mild
`psoriasis by self-report (eg, BSA \3%). Agreement
`between the two dermatologists on the presence of
`psoriasis for all subjects evaluated was only fair29
`(k 0.36, P \ .001) and both dermatologists agreed
`only 17% of the time in previously undiagnosed
`individuals. However, agreement between the two
`dermatologists among photographs of subjects who
`self-reported the presence of psoriasis via question-
`naire was moderate29 (k 0.54, P \ .001), and agree-
`ment among subjects with the most extensive disease
`([10% BSA) was perfect (k 1.0, P = .02).
`To determine prevalence estimates and measures
`of association, the raw data were adjusted for the
`sampling technique (Table I). The prevalence of
`psoriasis based on patient report of a healthcare
`provider diagnosis of the disease was similar in men
`and women and is estimated to be 3.15% (95% CI,
`2.18-4.53) of the US population aged 20-59 years.
`
`The prevalence of undiagnosed active psoriasis is
`estimated to be 0.4% (95% CI, 0.19- 0.82) based on a
`conservative definition (eg, both evaluators needed
`to confirm the presence of psoriasis). The prevalence
`of undiagnosed active psoriasis based on a less
`conservative definition (eg, at least one of the two
`evaluators needed to confirm the presence of psori-
`asis) was 2.28% (95% CI, 1.47-3.50) of the US pop-
`ulation aged 20-59 years.
`Table I also summarizes characteristics of patients
`with previously diagnosed psoriasis compared with
`patients who have undiagnosed active psoriasis.
`Subsequent analyses were conducted to determine
`which factors were associated with not receiving a
`previous diagnosis of psoriasis. Although not statis-
`tically significant because of a small sample size,
`regression analysis adjusted for age and sex showed
`a trend toward a greater likelihood of being male
`(OR, 5.72; 95% CI, 0.49-67.35), non-white (OR, 1.34;
`95% CI, 0.20-8.83), less educated (OR, 3.78; 95% CI,
`0.64-22.37), and not married (OR, 1.70; 95% CI, 0.26-
`11.05) in patients with undiagnosed active psoriasis
`
`Page 00004
`
`

`

`222 Kurd and Gelfand
`
`J AM ACAD DERMATOL
`FEBRUARY 2009
`
`Table II. Extent of psoriasis severity and impact on daily life in patients with history of a healthcare provider
`diagnosis of psoriasis*
`
`Moderate to severe psoriasis
`Mild psoriasis
`Little/no psoriasis 1%-2% BSA psoriasis 3%-10% BSA psoriasis [10% BSA psoriasis
`
`51.59%
`Proportion of psoriasis patients
`Mean psoriasis impact on daily life (95% CI) 3.22 (2.37-4.07)
`
`31.68%
`4.11 (2.97-5.25)
`
`11.38%
`7.32 (5.31-9.32)
`
`5.25%
`10 (10.0-10.0)
`
`BSA, Body surface area.
`*Of psoriasis patients with a history of physician diagnosis, 83.37% had mild psoriasis (little/no to 1%-2% BSA), whereas 16.63% had
`moderate to severe disease ( $ 3% BSA). Mean psoriasis impact on daily life score increased with increasing psoriasis severity.
`
`confirmed by both dermatologists compared to pa-
`tients with a previous diagnosis of psoriasis. Patients
`with undiagnosed psoriasis based on the less con-
`servative definition were more likely to be male (OR,
`4.29; 95% CI, 2.34-7.87), non-white (OR, 2.12; 95%
`CI, 1.00-4.48), have a lower household income (OR,
`2.46; 95% CI, 1.02-5.95), be less educated (OR, 3.51;
`95% CI, 1.39-8.88), and not married (OR, 2.65; 95%
`CI, 1.39-5.07) compared to patients who had re-
`ceived a diagnosis. Health insurance status was not
`associated with having newly diagnosed psoriasis
`(OR, 1.83; 95% CI, 0.73-4.61).
`Patients with a history of healthcare providere
`diagnosed psoriasis were asked to provide informa-
`tion on the extent of their psoriasis as well as how
`psoriasis impacts their daily life. Psoriasis impact on
`daily life was scored from 1-10 where 1 indicates no
`impact and 10 indicates severe impact (Table II). In
`analysis of the extent of psoriasis on daily life,
`previously established categories were applied (1-3,
`little or no problem; 4-7, a problem; 8-10, a large
`problem).24 More than half (56.66%) of all psoriasis
`patients with a previous diagnosis reported that
`psoriasis was a little or no problem in their daily
`lives, whereas 18.44% reported that it was a problem
`and 24.91% reported that it was a large problem. It is
`estimated that 83.37% of the previously diagnosed
`psoriasis population has limited skin disease (\3%
`BSA) while 16.63% are estimated to suffer from more
`moderate to severe disease ( $ 3% BSA). After ad-
`justment for age and gender, the extent to which
`psoriasis impacts daily life was associated with pso-
`riasis severity (P \.001 for trend). For example, 16%
`of patients with mild psoriasis rated it as a large
`problem, whereas 72% of moderate to severe psori-
`asis patients rated it as a large problem.
`
`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 photo-
`graphs 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, this study
`confirms that a substantial number of psoriasis
`patients suffer from disease which is severe enough
`to warrant systemic therapy based on current con-
`sensus statements.7,8 For example, about 17% have
`moderate to severe psoriasis based on BSA estimates,
`and 25% of patients rate psoriasis as a large problem
`in everyday life. Furthermore, we determined that by
`conservative estimates approximately 0.4% (2.28%
`based on a less strict definition) of the general
`population aged 20-59 years have undiagnosed,
`clinically active psoriasis. Importantly, our analyses
`demonstrate that significant disparities may exist
`among psoriasis patients in terms of the likelihood
`that
`they have been previously diagnosed by a
`healthcare provider. In particular, people with undi-
`agnosed active psoriasis may be more likely to be
`male, unmarried, non-white,
`and have
`less
`education.
`With application of these prevalence estimates to
`the population at the time these data were collected,
`it is estimated that approximately 5 million people
`20-59 years of age have been previously diagnosed
`with psoriasis and that, despite having active disease,
`an additional 600,000 (conservative estimate) to 3.6
`million people have psoriasis but remain undiag-
`nosed. Furthermore, we estimate that 1.4 million
`patients aged 20-59 years have moderate to severe
`disease and that 2.1 million consider psoriasis to be a
`large problem in daily life.
`A particular strength of this study is that NHANES
`participants are selected in a manner that is repre-
`sentative of the general US population. In addition,
`interviews and examinations are conducted on site at
`people’s homes and participation rates are favorable
`to other published reports of the prevalence of
`psoriasis.9,30 As with any study, there are important
`limitations to consider. As NHANES interviewers and
`examiners were unaware of our hypothesis to be
`tested,
`it is unlikely that any misclassification of
`covariates measured was directional
`(ie that
`
`Page 00005
`
`

`

`J AM ACAD DERMATOL
`VOLUME 60, NUMBER 2
`
`Kurd and Gelfand 223
`
`misclassification was more likely to occur in subjects
`who had psoriasis than those who did not), and
`therefore any such misclassification would bias our
`findings toward the null. Furthermore, the sample
`size of this study was not large enough to perform
`analyses in certain subpopulations, and many esti-
`mates were subject to imprecision (eg, wide confi-
`dence intervals).
`A particular challenge to conducting epidemio-
`logical studies in psoriasis is that there is no univer-
`sally agreed upon ‘‘gold standard’’ case definition of
`psoriasis which is readily applied in the setting of
`a broadly representative population-based study.
`Patient interview (questionnaire) data are commonly
`used, but are based on self-reports and are therefore
`subject to errors such as recall bias (forgetting a
`previous diagnosis or recalling a diagnosis which did
`not occur), misunderstanding of the question, in-
`ability to identify cases which have not received a
`medical diagnosis, and various other factors which
`can result in an underestimate or overestimate of the
`prevalence of psoriasis. Nevertheless, patient recall
`of chronic medical conditions has generally been
`shown to be accurate and use of selfereport of a
`psoriasis diagnosis has been well accepted in previ-
`ous epidemiological studies.9,24,31,32
`To address the limitation of self-report of a
`physician diagnosis of psoriasis, NHANES also eval-
`uated prevalence of psoriasis based on review of
`standardized clinical photographs by two dermatol-
`ogists. As a tool to detect psoriasis in the general
`population, this method was limited by only fair
`agreement about the presence of psoriasis in the
`standardized photographs by the two reviewing
`dermatologists. The results of this study also indicate
`that standardized photographs are significantly less
`likely to detect psoriasis that affects a limited BSA
`(eg, #2%). This limitation is problematic given that
`the overwhelming majority of psoriasis cases are
`mild or potentially in remission in the general
`population, as demonstrated by the current and
`previous studies.24 Furthermore,
`in the NHANES
`study anatomic areas such as the chest, abdomen,
`feet, scalp, buttock, and groin were not photo-
`graphed, which could also result in not identifying
`cases of psoriasis. Several factors such as disease that
`is limited, in remission, or located on anatomic sites
`not photographed may lead to an underestimate of
`the true prevalence of undiagnosed psoriasis based
`on the NHANES data.
`Review of standardized photographs was much
`more likely to confirm psoriasis in those with higher
`self-reported BSA of involvement, and agreement
`was excellent in those with the most severe psoriasis
`(eg, BSA $10%), suggesting that photography may
`
`be a valid method for detecting severe disease in the
`general population.
`In conclusion, this study demonstrates that psori-
`asis is common and is associated with a substantial
`health burden in a significant percentage of cases.
`Importantly, our results suggest that a large number
`of patients with active psoriasis remain undiagnosed
`and that a variety of socioeconomic disparities may
`explain why psoriasis may be undiagnosed.
`Additional studies are needed to better define the
`prevalence of undiagnosed psoriasis and to deter-
`mine what barriers exist which prevent these pa-
`tients from receiving medical care for this important
`disease.
`
`We are indebted to Daniel B. Shin for his help with
`data analysis.
`
`REFERENCES
`1. Azfar RS, Gelfand JM. Psoriasis and metabolic disease: epide-
`miology and pathophysiology. Curr Opin Rheumatol 2008;20:
`416-22.
`2. Gelfand JM, Troxel AB, Lewis JD, Kurd SK, Shin DB, Wang X,
`et al. The risk of mortality in patients with psoriasis: results
`from a population-based study. Arch Dermatol 2007;143:1493-
`9.
`3. Gelfand JM, Neimann AL, Shin DB, Wang X, Margolis DJ, Troxel
`AB. Risk of myocardial
`infarction in patients with psoriasis.
`JAMA 2006;296:1735-41.
`4. Neimann AL, Shin DB, Wang X, Margolis DJ, Troxel AB, Gelfand
`JM. Prevalence of cardiovascular risk factors in patients with
`psoriasis. J Am Acad Dermatol 2006;55:829-35.
`5. Kurd S, Richardson S, Gelfand J. An update on the epidemi-
`ology and systemic treatment of psoriasis. Expert Rev Clin
`Immunol 2007;3:171-85.
`6. Gelfand JM, Azfar RS, Shin DB, Kurd SK, Wang X, Troxel AB.
`Incidence of stroke in patients with psoriasis: a populatione
`based study. J Invest Dermatol 2008;128:S81.
`7. Pariser DM, Bagel J, Gelfand JM, Korman NJ, Ritchlin CT,
`Strober BE, Van Voorhees AS. National Psoriasis Foundation
`clinical consensus on disease severity. Arch Dermatol 2007;
`143:239-42.
`8. Gelfand JM. Long-term treatment for severe psoriasis: we’re
`halfway there, with a long way to go. Arch Dermatol 2007;143:
`1191-3.
`9. Koo J. Population-based epidemiologic study of psoriasis with
`emphasis on quality of life assessment. Dermatol Clin 1996;14:
`485-96.
`10. Johnson M, Roberts J. Skin conditions and related need for
`medical care among persons 1-74 years. United States, 1971-
`1974. Vital Health Stat 1978;11:72.
`11. Nevitt GJ, Hutchinson PE. Psoriasis in the community: preva-
`lence, severity and patients’ beliefs and attitudes towards the
`disease. Br J Dermatol 1996;135:533-7.
`12. Yip SY. The prevalence of psoriasis in the Mongoloid race.
`J Am Acad Dermatol 1984;10:965-8.
`13. Gelfand JM, Weinstein R, Porter SB, Neimann AL, Berlin JA,
`Margolis DJ. Prevalence and treatment of psoriasis in the
`United Kingdom: a population-based study. Arch Dermatol
`2005;141:1537-41.
`14. Psoriasis Hellgren L. A statistical, clinical and laboratory
`investigation of 255 psoriatics and matched healthy controls.
`Acta Derm Venereol 1964;44:191-207.
`
`Page 00006
`
`

`

`224 Kurd and Gelfand
`
`J AM ACAD DERMATOL
`FEBRUARY 2009
`
`15. Kavli G, Stenvold SE, Vandbakk O. Low prevalence of psoriasis
`in Norwegian lapps. Acta Derm Venereol 1985;65:262-3.
`16. Ferrandiz C, Bordas X, Garcia-Patos V, Puig S, Pujol R, Smandia
`A. Prevalence of psoriasis in Spain (Epiderma Project: phase I).
`J Eur Acad Dermatol Venereol 2001;15:20-3.
`17. Lomholt G. Psoriasis on the Faroe Islands; a preliminary report.
`Acta Derm Venereol 1954;34:92.
`18. Barisic-Drusko V, Paljan D, Kansky A, Vujasinovic S. Prevalence
`of psoriasis in Croatia. Acta Derm Venereol Suppl (Stockh)
`1989;146:178-9.
`19. Brandrup F, Green A. The prevalence of psoriasis in Denmark.
`Acta Derm Venereol 1981;61:344-6.
`20. Naldi L. Epidemiology of psoriasis. Curr Drug Targets Inflamm
`Allergy 2004;3:121-8.
`21. Falk ES, Vandbakk O. Prevalence of psoriasis in a Norwegian
`Lapp population. Acta Derm Venereol Suppl (Stockh) 1993;
`182:6-9.
`22. Rea JN, Newhouse ML, Halil T. Skin disease in Lambeth. A
`community study of prevalence and use of medical care. Br J
`Prev Soc Med 1976;30:107-14.
`23. Gelfand JM, Stern RS, Nijsten T, Feldman SR, Thomas J, Kist J,
`et al. The prevalence of psoriasis in African Americans: results
`from a population-based study. J Am Acad Dermatol 2005;52:
`23-6.
`24. Stern RS, Nijsten T, Feldman SR, Margolis DJ, Rolstad T.
`Psoriasis is common, carries a substantial burden even when
`
`not extensive, and is associated with widespread treatment
`dissatisfaction. J Investig Dermatol Symp Proc 2004;9:136-9.
`25. Neimann AL, Porter SB, Gelfand JM. The epidemiology of
`psoriasis. Expert Rev Dermatol 2006;1:63-75.
`26. Kavli G, Forde OH, Arnesen E, Stenvold SE. Psoriasis: familial
`predisposition and environmental factors. Br Med J (Clin Res
`Ed) 1985;291:999-1000.
`27. Gelfand JM, Feldman SR, Stern RS, Thomas J, Rolstad T, Margolis
`DJ. Determinants of quality of life in patients with psoriasis: a study
`from the US population. J Am Acad Dermatol 2004;51:704-8.
`28. National Psoriasis Foundation. About psoriasis: statistics.
`Available at: http://www.psoriasis.org/about/stats/. Accessed
`November 6, 2008.
`29. Landis JR, Koch GG. The measurement of observer agreement
`for categorical data. Biometrics 1977;33:159-74.
`30. Gelfand JM, Gladman DD, Mease PJ, Smith N, Margolis DJ,
`Nijsten T, et al. Epidemiology of psoriatic arthritis in the
`population of the United States. J Am Acad Dermatol 2005;53:
`573.
`31. Feldman SR, Fleischer AB Jr, Reboussin DM, Rapp SR, Exum
`ML, Clark AR, et al. The self-administered psoriasis area and
`severity index is valid and reliable. J Invest Dermatol 1996;106:
`183-6.
`32. Martin LM, Leff M, Calonge N, Garrett C, Nelson DE. Validation
`of self-reported chronic conditions and health services in a
`managed care population. Am J Prev Med 2000;18:215-8.
`
`Page 00007
`
`