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EXTENDED REPORT
High prevalence of psoriatic arthritis in patients with
severe psoriasis with suboptimal performance of
screening questionnaires
Muhammad Haroon,
1
Brian Kirby,
2
Oliver FitzGerald
1
▸ Additional data are
published online only. To view
this file please visit the journal
online (http://ard.bmj.com)
1
Department of Rheumatology,
St Vincent’s University
Hospital, Dublin, Ireland
2
Department of Dermatology,
St Vincent’s University
Hospital, Dublin, Ireland
Correspondence to
Professor Oliver FitzGerald,
Department of Rheumatology,
St Vincent’s University
Hospital, Elm Park, Dublin,
4, Ireland;
oliver.fitzgerald@ucd.ie
Received 19 March 2012
Accepted 20 May 2012
ABSTRACT
Objectives The objectives of this study were to: (1)
assess the prevalence of psoriatic arthritis (PsA) among
Psoriasis (Ps) patients attending dermatology clinics;
(2) identify clinical predictors of the development of PsA;
and (3) compare the performance of three PsA screening
questionnaires: Psoriatic Arthritis Screening and
Evaluation (PASE), Psoriasis Epidemiology Screening Tool
(PEST) and Toronto Psoriatic Arthritis Screening (ToPAS).
Methods Pa t ients wer e divided into two groups: Group-1,
consecutive psoriasis patients attending derma tology clinics
with no known diagnosis of inflammatory arthritis and
Group-2, consecutive patients attending rheumatology
clinics with a confirmed diagnosis of PsA. In Group-1,
patients completed the scr e ening questionnaires, followed
by a full rheuma t ological evalua t ion whether or not they
reported musculosk eletal symptoms.
Results 200 patients wer e recruited with 100 in each
group. In all, 84% of patients in dermatology group wer e
using sy stemic therapy for their skin disease, and 99% of
patients in rheumatology group were on systemic
immunosuppressiv es. In Group-1, 29% of patients were
diagnosed with PsA after rheumatological evaluation. On
univariate and multivariate analyses, there was a significant
positive association between Psoriasis Area and Severity
Index and a new diagnosis of PsA ( p=0.046). Different
patterns of joint involvement wer e noted in patients with
newly diagnosed PsA versus patients with established PsA
with few er polyarticular disease presentations ( p=0.0001).
In Group-1, the PEST, PASE and ToPAS assessments had
sensitivities of 27.5%, 24% and 41%, and specificities of
98%, 94% and 90%, respectiv ely. In Group-2, the
sensitivities were 86%, 62% and 83%, respectiv ely.
Conclusions 29% of Ps patients attending dermatology
clinics had undiagnosed PsA. Psoriasis severity was
associated with a new diagnosis of PsA. Poor sensitivities
for the screening questionnaires wer e noted due to
inadequate detection of patterns of arthritis other than
polyarticular disease.
INTRODUCTION
Psoriatic arthritis (PsA) is a progressive inflamma-
tory joint disease, causing pain and joint damage
eventually leading to disability. Up to 47% of
patients develop erosive changes within 2 years of
disease onset.
1
There are varied reports of its preva-
lence among patients with psoriasis, with the
prevalence rates ranging from 6% to 42%.
2
The
severity of psoriasis has been regarded as a poor
clinical predictor of the development and severity
of PsA;
2
however, a recent report has suggested the
opposite results.
3
Similar to patients with rheumatoid arthritis,
early diagnosis and institution of disease modifying
antirheumatic drug treatment have been shown to
have an impact on long-term morbidity.
4
The dela y
in the diagnosis of PsA however remains a significant
contributor to poor patient outcomes (online supple-
mentary appendix). The early identifica tion of
patients with PsA among patients with psoriasis
therefore assumes considerable importance. Patients
with psoriasis are usually managed by general practi-
tioners or by dermatologists who can either rely on
self-reported joint symptoms to identify PsA or can
be more proactive in elucidating the appropriate
musculoskeletal (MSK) symptoms and signs. Both
approaches pr esent difficulties with patients failing
to appreciate the relevance of their symptoms and
time constraints on general practitioners and derma-
tologists that hinder appropriate assessment. It is
neither appropriate nor practical to seek rheumatolo-
gist opinion for all psoriasis patients in order to
assess for the development of PsA. Screening ques-
tionnaires have been developed as referral tools to
help dermatologists and general practitioners identify
suitable individuals for referral to rheumatologists.
These screening tools include the Psoriatic Arthritis
Screening and Evaluation (PASE), Psoriasis
Epidemiology Screening Tool (PEST) and the Toronto
Psoriatic Arthritis Screening (ToPAS).
5–8
As these are
not diagnostic tools, individuals identified by such
screening tools as likely candidates must then
undergo further rheumatological evaluation in order
that a definitive diagnosis can be made. The screen-
ing tools have undergone initial validation at the
centres where they were developed with some add-
itional validation being provided in subsequent
studies.
5–10
To our knowledge, sensitivity and specifi-
city of these tools versus the gold standard of a full
rheumatological evaluation has not been compared
in psoriasis patients attending dermatology clinics.
The aims of this study wer e threefold: (1) to assess
the pr evalence of undiagnosed PsA among patients
atten ding dermatology clinics, (2) to e xplor e the
impact of demogr aphics and different disease specific
char a cte ris tics on the development of PsA and (3) to
compar e the performance and utility of the three PsA
questionnair es (PASE, PEST, and the ToPAS) versus a
full rheumatological evalua tion using CASPAR criteria
(Criteria of the ClASsification of Psoriatic ARthritis)
in psoriasis patients attending dermatology clinics.
Ann Rheum Dis 2012;0:1–5. doi:10.1136/annrheumdis-2012-201706 1
Clinical and epidemiological research
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METHODS
This study was carried out in the general dermatology and
rheumatology clinics based at St. Vincent’s University Hospital,
Dublin, Ireland. We divided patients into two groups: Group-1,
patients with skin psoriasis attending dermatology clinics who
have no known diagnosis of arthritis and Group-2, patients
attending rheumatology clinic with a confirmed diagnosis of PsA
as per the internationally agreed CASPAR criteria.
11
All consecu-
tive psoriasis patients attending dermatology clinics, but who did
not have a diagnosis of PsA, were suitable for inclusion.
Consecutive patients attending rheumatology clinics with a con-
firmed diagnosis of PsA were also eligible to partake. Patients with
a concomitant MSK condition, such as osteoarthritis, gout and
fibromyalgia, were not excluded in both dermatology and rheuma-
tology groups, but we did exclude those patients with a history of
other inflammatory arthropathies, such as rheumatoid arthritis.
The study was approved by the Medical Research Ethics
committee of St. Vincent’s University Hospital. Informed
written consent was obtained from patients before inclusion in
the study (Methods have been described in more detail in the
online supplementary appendix). The assessment of psoriatic
patients enrolled in Group-1 was carried out in two steps. The
first step involved completing the questionnaires (PEST, PASE,
ToPAS), and documentation of the following clinical details:
demographics, therapies used for psoriasis, duration of skin
disease, presence of nail involvement, and the extent and sever-
ity of skin psoriasis as reflected by the Psoriasis Area and
Severity Index (PASI), which is the most widely used tool for
the measurement of severity of psoriasis. In the second step, all
patients received a full rheumatological evaluation, whether or
not they reported any MSK symptoms. The rheumatological
parameters evaluated included joint counts (tender, swollen,
damaged), entheseal counts using the Leeds Enthesitis Index
and including evaluation of the plantar fascia insertion, dactyli-
tic counts and history taking and examination for axial inflam-
matory joint disease. The final diagnosis of PsA in Group-1 was
made by the fulfilment of CASPAR classification criteria (online
supplementary appendix). To observe the pattern of initial pres-
entation and to compare this with the group of established PsA
patients, we categorised PsA patients into four main categories
depending on the predominant type of arthritis. These categor-
ies include: polyarthritis (≥5 joints affected), oligoarthritis (≤4
joints affected), predominant entheseal involvement and pre-
dominant inflammatory axial involvement. The questionnaires
were not marked prior to rheumatological assessment, and
hence, the rheumatologist assessing these psoriatic patients
was unaware of the results of questionnaires. Questionnaires
were marked and scored for questionnaire positivity or negativ-
ity. For this study, previously established cut-off scores were
used to designate positive and negative results for each screen-
ing tool. The sensitivities and specificities of these question-
naires were determined by comparing the results with the
rheumatological diagnostic assessment using CASPAR criteria.
Statistical analysis
Statistical analysis was performed using the SPSS software,
V.17. Significance was defined as p<0.05 (two-tailed). A χ
2
stat-
istic was used to investigate the distributions of categorical
variables, and continuous variables were analysed using
Student t test. The association among psoriasis extent, dur-
ation of psoriasis, nail disease, therapies used for psoriasis, use
of TNFi (Tumour necrosis Factor inhibitors), age and sex with
newly diagnosed PsA was determined by using univariate and
multivariate logistic regression.
The efficacy of screening tools in predicting a diagnosis of
PsA was measured in terms of sensitivity and specificity.
Sensitivity indicates the probability that someone with PsA
would have tested positive on these questionnaires; specificity
refers to the probability that someone without PsA would have
tested negative on these questionnaires. Positive predictive
value and negative predictive value were also determined,
which reflect the probability of how likely a patient with a
positive or negative test result actually has or does not have the
particular disease.
RESULTS
In all, 200 patients were recruited of whom 100 were from the
dermatology clinics (Group-1) and 100 were from the rheumatol-
ogy clinics (Group-2). Table 1 illustrates the demographic details
and clinical characteristics of these two groups. It was noted that
Group-1 patients had significantly more severe psoriasis (PASI),
more scalp psoriasis at the time of assessment and less nail
disease ever in the disease course compared with Group-2. In all,
84% of patients in dermatology group were using systemic
therapy for their skin disease, and 99% of patients in rheumatol-
ogy group were on systemic immunosuppressives.
In Group-1, 29% of patients were diagnosed with PsA after
rheumatological evaluation (Results have been described in
more detail in the results section of online supplementary
appendix). Table 2 compares the demographic and clinical
details of these newly diagnosed PsA patients with those who
had no PsA. This subgroup analysis revealed that newly diag-
nosed PsA patients had more severe psoriasis as measured by
PASI. There was no significant difference as regards age, gender,
medications used for psoriasis, duration of skin psoriasis and
nail disease. We also compared the clinical characteristics of
newly diagnosed PsA patients with the established PsA patients
of Group-2 (table 3). This revealed that the pattern of joint
involvement was significantly different with less polyarticular
disease in newly diagnosed PsA patients.
Table 1 Demographic and clinical characteristics of the two patient
cohorts
Group-1 (dermatology
patients, n=100)
Group-2 (rheumatology
patients, n=100) p Value
Age (years±SD) 52.30±13.32 49.57±12.51 0.59
Gender, % male 64 49
Medications TNF inhibitors=39 TNF inhibitors=53
Fumaderm=35 Synthetic DMARDs=36
Phototherapy=12 Others=11
Ustekinumab=3
Ciclosporin=2
Methotrexate=2
Others=7
Duration of
psoriasis (years
±SD)
28.9±14.45 25.38±13.75 0.62
PASI (score±SD) 2.044±1.15 1.65±2.33 0.001
% Nail disease,
current
68 77 0.15
% Nail disease,
ever
72 84 0.041
% Scalp psoriasis,
current
56 17 <0.0001
% Scalp psoriasis,
ever
91 82 0.06
DMARD, disease modifying antirheumatic drug; PASI, Psoriasis Area and Severity
Index; TNF, tumour necrosis factor.
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On univariate and multivariate analyses, the only signi fi-
cantly positive association was noted between PASI and
the new diagnosis of PsA (OR 1.45 (95% CI 1.00 to 2.11),
p=0.05, and OR 1.61 (95% CI 1.06 to 2.44), p=0.02, respect-
ively), even after adjusting for confounders such as age, gender,
use of TNFi (Tumour Necrosis Factor inhibitor), duration of
psoriasis and the presence of nail and scalp disease ever in the
disease course (table 4).
Table 5 shows the sensitivity, specificity, positive predictive
value and negative predictive value of the three screening ques-
tionnaires. In Group-1, the PEST, PASE and ToPAS had sensitiv-
ities of only 27.5%, 24% and 41%, respectively; however, the
sensitivities of these three screening tools in Group-2 were
86%, 62% and 83%, respectively. We also looked at the sensitiv-
ity and specificity of lower cut-off points for each questionnaire
(online supplementary appendix). We also examined whether
these questionnaires differ in their performance depending on
the subtype of arthritis present. This analysis showed that the
PEST and ToPAS questionnaires had comparatively better sensi-
tivities in identifying PsA patients with polyarticular involve-
ment (77% and 88%. respectively), but their sensitivities were
low for any other non-polyarticular disease presentations (5%
and 20%, respectively). The PASE questionnaire had poor per-
formance for both polyarticular and non-polyarticular disease
(sensitivity of 22% and 20%, respectively) (table 6).
DISCUSSION
The delay in the diagnosis of PsA remains a significant con-
tributor to poor patient outcome thus highlighting the need to
improve our evaluation of patients who are at risk for articular
disease. The results of our study are important in a number of
ways. First, we found that after excluding patients with known
PsA, 29% of psoriasis patients attending dermatology clinics
had undiagnosed PsA. These prevalence rates are significantly
higher than in previous reports, which reveal undiagnosed PsA
in 17%, and both diagnosed and undiagnosed PsA in 30%.
12 13
Second, we noted also that severity of skin disease is independ-
ently associated with the development of PsA. Our study was
carried out in a routine dermatology clinical setting, where the
majority of psoriasis patients being followed used systemic
therapies. It was surprising to note such a high prevalence of
PsA since a significant numbers of patients were already using
Table 3 Comparison of demographics and clinical characteristics of patients who had newly diagnosed psoriatic arthritis (PsA) with those who had
established PsA
Newly diagnosed patients with PsA (n=29) Known PsA patients (n=100) p Value
Age (years±SD) 52.03±10.62 49.57±12.51 0.43
% Male 18 (62%) 49 (49%) 0.21
Duration of psoriasis (years±SD) 29.10±15.08 25.38±13.75 0.84
Duration of PsA (years±SD) 1.05±0.66 14.46±10.39 <0.0001
PASI (score±SD) 2.40±1.13 1.65±2.33 0.02
Nail disease, current (%) 20 (69%) 77 (77%) 0.37
Nail disease, ever (%) 22 (76%) 83 (83%) 0.38
Scalp Ps, current (%) 15 (52%) 17 (17%) <0.0001
Scalp Ps, ever (%) 27 (93%) 82 (82%) 0.14
Active joint disease (%) 26 (89.65%) 36 (36%) <0.0001
Predominant type of arthritis
Polyarthritis (≥5 joints) 9 (31%) 75 (75%) <0.0001
Oligoarthritis (≤4 joints) 9 (31%) 17 (17%)
Enthesitis 4 (14%) 0 (0%)
Inflammatory axial disease 7 (24%) 8 (8%)
PASI, Psoriasis Area and Severity Index; Ps, psoriasis.
Table 2 Comparison in Group-1 of demographics and clinical characteristics of patients who had undiagnosed psoriatic arthritis (PsA) with those
who had no PsA
Newly diagnosed patients with PsA (n=29) Patients who had no PsA (n=71) p Value
Age (years±SD) 52.03±10.62 52.41±14.34 0.89
Male (%) 18 (62%) 46 (65%) 0.79
On systemic therapy
TNF inhibitors 10 (34%) 29 (41%) 0.74
Fumaderm 11 (38%) 24 (34%)
Phototherapy 3 (10%) 9 (13%)
Ustekinumab 1 (3%) 2 (3%)
Ciclosporin 0 2 (3%)
Duration of psoriasis (years±SD) 29.10±15.08 28.82±14.29 0.92
PASI (score±SD) 2.40±1.13 1.89±1.14 0.04
Nail disease, current (%) 20 (69%) 48 (67.6%) 0.35
Nail disease, ever (%) 23 (79%) 49 (69%) 0.06
Scalp Ps, current (%) 15 (52%) 41 (58%) 0.58
Scalp Ps, ever (%) 27 (93%) 64 (90%) 0.16
PASI, Psoriasis Area and Severity Index; TNF, tumour necrosis factor; Ps, psoriasis.
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TNFi (Tumour Necrosis Factor inhibitor) and disease modifying
antirheumatic drugs, which are treatments of choice for PsA
and may have masked the development of articular involve-
ment. It is possible that in the absence of such therapies, the
prevalence of PsA would have been higher (online supplemen-
tary appendix). In our cohort, when we compared the extent
of skin involvement of newly diagnosed PsA patients with
those who had no PsA in Group-1, the PASI was significantly
higher in newly diagnosed patients with PsA. We investigated
this further by using univariate and multivariate regression
models and noted that psoriasis severity was an independent
predictor of undiagnosed PsA among psoriasis patients after
adjusting for all factors in the model which included age,
gender, use of TNFi (Tumour Necrosis Factor inhibitor), dur-
ation of psoriasis and the presence of nail and scalp disease ever
in the disease course.
Third, and consistent with previous reports,
14–16
we found
that the presence of psoriatic nail disease ever in the disease
course was significantly higher in established PsA patients
(Group-2) versus Group-1 (p=0.041). A trend was also seen in
newly diagnosed PsA patients with a non-significant associ-
ation when compared with those who had no PsA (p=0.065).
The presence of nail disease at the time of assessment was not
statistically different among all cohorts: Group-1 versus
Group-2, or newly diagnosed PsA patients versus those who
had no PsA in Group-1. It is possible that the use of systemic
therapies which may be effective for nail psoriasis is an explan-
ation for this observation. It should be noted that the CASPAR
criteria only accept nail disease if evident on current physical
examination. The screening questionnaire PEST attributes a
fifth of its total score if a patient has current nail changes.
8
Fourth, the presence of scalp disease ever in the disease
course was found to be statistically similar in all cohorts. When
compared with Group-2, Group-1 patients had higher incidence
of scalp psoriasis at the time of assessment, probably reflecting
more severe psoriasis. In contrast to previous reports,
15 16
there
was no difference in the prevalence of current scalp psoriasis
between Group-1 patients with newly diagnosed PsA and those
with psoriasis only.
15 16
Finally, our study showed poor sensitivities for the three
screening questionnaires for PsA. This observation is of import-
ance as PsA is no longer considered as a mild form of arthritis.
In one study, 67% of PsA patients demonstrated ≥1 radio-
graphic erosion at their initial presentation to a rheumatolo-
gist.
17
In an inception cohort study, Kane et al
1
found that 47%
of their patients with early arthritis who presented within
5 months of onset of symptoms had ≥1 erosion by the second
year of follow-up. These study results have important implica-
tions for the use of these instruments for screening purposes
(online supplementary appendix). It would appear that the
questionnaires in particular performed poorly in identifying
patients with non-polyarticular presentations of PsA.
Modification of the current questionnaires or development of a
new questionnaire to reflect these observations is required if
these screening tools are to be useful in identifying early PsA
among the large population of psoriasis patients. We believe
that the main thrust and focus of screening tools should be in
dermatology clinics as dermatologists assess and treat patients
with more severe psoriasis who are at risk for developing PsA.
The strengths of our study include the following: (1) to
reduce the possible confounding effect of differences in access
to healthcare services, this study was carried out in one second-
ary care dermatology/rheumatology setting; (2) to minimise
the selection bias, we have attempted to recruit all consecutive
patients; and (3) to standardise the study procedures, all
patients were reviewed by a single, trained rheumatologist. We
acknowledge there are some limitations to our study. For
example, we did not include other known risk factors for psor-
iasis and PsA, such as body mass index, presence of psoriasis at
intergluteal regions and alcohol consumption. No data were
collected on the functional impairment of both groups. x-Rays
were requested only in suspected cases of PsA; however, no
imaging studies were used to confirm the clinical diagnosis of
enthesopathies. In addition, our study population was receiving
Table 4 Univariate and multivariate (adjusted simultaneously for variables shown) associations of different clinical variables with the development
of psoriatic arthritis
Univariate model Multivariate model
OR* 95% CI p Value OR* 95% CI p Value
Age 0.99 0.96 to 1.03 0.89 0.99 0.95 to 1.02 0.61
Male gender 1.12 0.46 to 2.75 0.79 1.43 0.55 to 3.71 0.46
Use of TNFi 0.76 0.31 to 1.87 0.55 0.50 0.18 to 1.39 0.18
PASI 1.45 1.00 to 2.11 0.05 1.61 1.06 to 2.44 0.02
Duration of Psoriasis 1.00 0.97 to 1.03 0.92 1.00 0.97 to 1.04 0.76
Nail disease, ever 1.06 0.42 to 2.70 0.89 1.92 0.65 to 5.64 0.23
Scalp Ps, ever 1.47 0.28 to 7.57 0.64 1.53 0.28 to 8.23 0.61
OR, odds ratio; PASI, Psoriasis Area and Severity Index; Ps, psoriasis.
Table 6 Comparative performance of screening tools for polyarticular
disease manifestation with non-polyarticular disease among newly
diagnosed psoriatic arthritis patients
Non-polyarticular disease
<0.0001 (n=20) (%)
Polyarticular disease
<0.0001 (n=9) (%) p Value
Sensitivities of
PEST 5 77 <0.0001
PASE 20 22 0.87
ToPAS 20 88 <0.0001
PASE, Psoriatic Arthritis Screening and Evaluation; PEST, Psoriasis Epidemiology
Screening Tool; ToPAS, Toronto Psoriatic Arthritis Screening.
Table 5 Performance of screening Questionnaires in unselected
psoriasis patients attending dermatology clinics (Group-1)
Sensitivity (%) Specificity (%) PPV (%) NPV (%)
PEST 27.5 98 88 76
PASE 24 94 63 75
ToPAS 41 9 0 63 82
NPV, negative predictive value; PPV, positive predictive value.
4 Ann Rheum Dis 2012;0:1–5. doi:10.1136/annrheumdis-2012-201706
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systemic therapy for their psoriasis, which could potentially
limit the generalisability of results to a more severe spectrum
of psoriatic disease.
CONCLUSIONS
Our study confirms the high prevalence of PsA in patients with
psoriasis with severity of skin involvement as a useful pre-
dictor. Poor sensitivity performance of the three available
screening tools was also observed. Improving the identification
of the predictors of PsA development and devising an effective
screening questionnaire would aid in the earlier diagnosis and
improving long-term patient outcome.
Contributors MH carried out the work, collection and interpretation of data and
manuscript drafting. BK and OF conceived the study, its design, coordination, data
interpretation and manuscript drafting and editing.
Competing interest None.
Conflict of interest None of the named authors has any conflicts of interest.
Patient consent Yes.
Ethics approval Ethics approval provided by the St. Vincent’s Healthcare Group,
Ethics and Medical Research Committee.
Provenance and peer review Not commissioned; externally peer reviewed.
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doi: 10.1136/annrheumdis-2012-201706
published online June 23, 2012Ann Rheum Dis
Muhammad Haroon, Brian Kirby and Oliver FitzGerald
questionnaires
suboptimal performance of screening
patients with severe psoriasis with
High prevalence of psoriatic arthritis in
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(DOIs) and date of initial publication.
publication. Citations to Advance online articles must include the digital object identifier
citable and establish publication priority; they are indexed by PubMed from initial
typeset, but have not not yet appeared in the paper journal. Advance online articles are
Advance online articles have been peer reviewed, accepted for publication, edited and
http://group.bmj.com/group/rights-licensing/permissions
To request permissions go to:
http://journals.bmj.com/cgi/reprintform
To order reprints go to:
http://group.bmj.com/subscribe/
To subscribe to BMJ go to:
group.bmj.com on June 29, 2012 - Published by ard.bmj.comDownloaded from
