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Rheumatol Int (2014) 34:227–234DOI 10.1007/s00296-013-2876-z

ORIGINAL ARTICLE

High prevalence of psoriatic arthritis in dermatological patients with psoriasis: a cross‑sectional study

Joerg C Henes · Eva Ziupa · Michael Eisfelder · Annette Adamczyk · Bjoern Knaudt · Felix Jacobs · Juergen Lux · Stefan Schanz · Gerhard Fierlbeck · Daniel Spira · Marius Horger · Lothar Kanz · Ina Koetter

Received: 1 August 2013 / Accepted: 28 September 2013 / Published online: 10 October 2013 © Springer-Verlag Berlin Heidelberg 2013

assessed. The diagnosis of PsA was made according to the CASPAR criteria, and imaging was performed in addi-tion. A total of 404 questionnaires were evaluated; 50.5 % answered ≥4 questions positively; 19.3 % had a history of PsA confirmed by a rheumatologist; and in 10.9 %, PsA or spondyloarthritis was newly diagnosed during the present study. This leads to an overall prevalence of PsA in patients with psoriasis of 30.2 %. The frequency of psoriatic arthri-tis in the present study is higher than expected from previ-ous studies in Germany. The prevalence is consistent with findings of a large observational survey from Scandinavia. Using the CASPAR criteria and imaging in all patients, cer-tainty of the diagnosis is very high. The GEPARD Ques-tionnaire is a helpful tool to identify people at risk for pso-riatic arthritis.

Keywords Epidemiology · Psoriatic arthritis · Psoriasis · Prevalence · GEPARD Questionnaire

Introduction

Psoriatic arthritis (PsA) belongs to the group of spondy-loarthritides and occurs with different manifestations, e.g. axial, peripheral (symmetrical or asymmetrical, oligo- or polyarthritis) or with enthesitis. Most patients first pre-sent at a dermatologist due to their skin manifestation, which most commonly appears earlier than the arthritis. As arthralgia is an unspecific and very common symptom, some dermatologists and especially the patients them-selves may not be aware of the possible PsA which may explain their musculoskeletal complaints. In a consider-able number of patients, the arthritis may not be diag-nosed and remain undiscovered for a considerable period of time.

Abstract The exact prevalence of psoriatic arthritis (PsA) among patients with psoriasis is still not conclusive. Data in the literature vary between 5.8 and 30 %. Objective of this study was to gain more information on the prevalence of PsA among patients with psoriasis in Germany. Between 09/2010 and 05/2011, consecutive patients from dermato-logical private practices and a university hospital with pso-riasis were asked to fill out the validated German Psoriatic Arthritis Diagnostic (GEPARD) Questionnaire. Patients who answered ≥4 questions with “yes” were invited to come for a rheumatological check up. Those patients who refused a rheumatological examination were counted as “absence of PsA”. Laboratory tests for inflammatory mark-ers as well as the severity of skin manifestations were

J. C. Henes · E. Ziupa · L. Kanz · I. Koetter Centre for Interdisciplinary Clinical Immunology, Rheumatology and Auto-inflammatory Diseases (INDIRA), Tuebingen, Germany

J. C. Henes (*) · E. Ziupa · L. Kanz · I. Koetter Department of Internal Medicine II (Hematology, Oncology, Immunology, Rheumatology, Pulmology), University Hospital, Otfried-Mueller-Str. 10, 72076 Tuebingen, Germanye-mail: joerg.henes@med.uni-tuebingen.de

M. Eisfelder Rottweil, Germany

A. Adamczyk · B. Knaudt · F. Jacobs · S. Schanz · G. Fierlbeck Department of Dermatology, University Hospital, Tuebingen, Germany

J. Lux Tuebingen, Germany

D. Spira · M. Horger Department of Interventional and Diagnostic Radiology, University Hospital, Tuebingen, Germany

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The exact prevalence of PsA among patients with psori-asis is still not conclusive, and its estimation varies between 5.8 and 30 % [1–8]. The recently published German Pso-riatic Arthritis Diagnostic (GEPARD) Questionnaire [9] is a validated questionnaire with 14 questions in German language. It was designed to optimise screening for poten-tial PsA among patients with psoriasis. Its sensitivity and specificity is 89 and 69 %, respectively, for those patients answering ≥4 questions with “yes”. The questionnaire is a self-rating instrument to be answered by the patient with-out any help from the physician or nurse. There are differ-ent diagnostic and classification criteria for PsA. The most recent CASPAR criteria [10] have an excellent sensitivity in both early and late disease [11]. Therefore, we decided for these criteria to diagnose those patients presumed to have PsA.

The objective of this study was to get more information on the prevalence of PsA among patients with psoriasis in Germany using the GEPARD screening tool.

Methods

Patient recruitment

Two dermatological outpatient clinics and 10 private der-matological practices in Baden-Wurttemberg, southern Germany, were asked to recruit patients for this cross-sec-tional study. The study was approved by the local ethics committee, and all patients gave written informed consent.

Between 09/2010 and 05/2011, consecutive patients with known psoriasis were asked to fill out the GEPARD Questionnaire (English version, see Table 1) during their time in the waiting room of the dermatologist and without help of the physician or any medical staff. Patients with all forms of psoriasis were included. The first 4 questions of the GEPARD Questionnaire focus on clinical signs of arthritis; questions 5–8 assess impairments in daily life, and questions 9–13 address the axial manifestation, whereas question 14 evaluates the duration of complaints. Patients who answered ≥4 questions with “yes” were contacted and invited to come for a rheumatological check up.

Those patients who refused to come for a rheumatologi-cal examination were counted as “absence of PsA”. Those patients with a previous diagnosis of arthritis (question no. 7 answered “yes”) were requested to fill out a second ques-tionnaire (not shown) which focused on (1) the first mani-festation and diagnosis of psoriasis and psoriatic arthri-tis, (2) the systemic treatment of PsA and (3) the current status of joint pain and activity of psoriasis using a visual analogue scale. A control sample of those patients was phoned to question the diagnosis, and only those doubtful were invited to come to attend the rheumatological outpa-tient clinic in Tuebingen. For clinical diagnosis of PsA, the CASPAR criteria were used [10].

The dermatologists were asked to assess the Psoriasis Area and Severity Index (PASI) [12] score or to rate the activity of the skin manifestation into 4 categories: 0–3: not active, mild, moderate or severe. Correspondingly, the PASI was grouped similar to an activity score: PASI

Table 1 English version of the GEPARD Questionnaire. Patients are asked to answer all questions without help of the physician and tick either “yes” or “no”. All positive answers from question 1–13 have to be summed up

Questions Yes No

Have you ever had arthralgia which was associated with joint swelling?

Have you ever had swelling of one whole finger/toe?

Have you ever had arthralgia which was associated with joint redness?

Did you ever feel stiffness of the joint when you woke up in the morning?(a) If yes, how long? ________ minutes

Did you ever think about having a joint disease?

Did you ever contact a doctor for your joint complaints?

Did anyone ever make the diagnosis (psoriatic) arthritis?

Have you ever received medication for the treatment of your joint complaints?

Did you ever suffer from back or low back pain for at least 3 days/week?If yes, was this back pain …

… worst during the early morning?

… improving during activity?

… lasting during rest?

… accompanied by morning stiffness?

If you have answered one of the questions “yes”: For how long do you suffer from these complaints?

More than 1 week More than 1 month More than 3 months More than 6 months More than 1 year More than 3 years More than 5 years

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0–1 = not active; PASI 2–10 = mild; 11–15 = moderate and >15 = severe.

Clinical assessment

All patients were seen by the same physician (JCH). After a careful medical history and physical examination with focus on manifestations of psoriasis, morning stiff-ness, joint pain and swelling, family history of psoriasis or rheumatic diseases as well as on differential diagnosis for arthralgia, blood samples were taken for erythrocyte sedimentation rate (ESR; mm/h), c-reactive protein (CRP; mg/dl), rheumatoid factor, anti-CCP antibodies, screening for anti-nuclear antibodies (ANA) by immunofluorescence and HLA B27.

For estimation of clinical activity, the disease activity score (DAS) 28/44 [13, 14], the Ankylosing Spondylitis Disease Activity Score (ASDAS [15]) and the Bath Anky-losing Spondylitis Metrology Index (BASMI [16]) were performed, depending on the clinical manifestations. In addition, all patients with axial manifestations were asked to fill out the Bath Ankylosing Spondylitis Disease Activity Index and Bath Ankylosing Spondylitis Functional Index (BASDAI/BASFI [17, 18]).

Radiographic assessment

In those patients with tender joints at the time of presen-tation, at least ultrasound of the most affected joints was performed always by the same physician (JCH) using a high-end ultrasound (MyLab70; ESAOTE; Italy) with a 9–13 MHz transducer. As synovitis and effusion is often mild in PsA, powerdoppler was added in all patients to recognise increased perfusion as a sign of inflammation. Synovitis with effusion and/or powerdoppler activity was judged active arthritis. PsA often presents with asymmet-ric oligoarthritis; therefore, no adequate ultrasound scoring system is available.

Most patients also underwent X-ray of the affected joints, usually hands or feet. Juxta-articular bony prolif-eration with or without erosions, dactylitis, periosteal new bone formation, pencil in cup phenomenon were counted typically for PsA [10].

Magnetic resonance imaging (MRI) using a 1.5 or 3.0 Tesla MRI (Espree or TRIO; Siemens Medical Solutions, Erlangen, Germany) was added in patients with unclear clinical and sonographical findings to verify or exclude the diagnosis of PsA and for those patients with suspected axial involvement. At least T1-weighted and T2- and T1-weighted gadolinium-enhanced sequences of the most painful joint were evaluated. Enthesitis, multifocal bone marrow oedema, periostitis and extracapsular enhancement accompanying articular or tendon sheath synovitis were regarded typical of

psoriatic arthritis [19]. No blinded imaging reading was per-formed, neither for X-ray nor for MRI.

Statistics

Statistical analysis was performed using SPSS for Win-dows, Version 19.0 (SPSS, Chicago, IL). All values are mean values ± standard deviation (SD) or median values with range. Significances were calculated using U test with p < 0.05 considered statistically significant. Prevalence was calculated by dividing the number of confirmed PsA patients by all patients. Patients with uncertain diagnosis or missing data were counted as absence of PsA.

Results

A total of 412 consecutive patients filled out the GEPARD Questionnaire, and 404 of those questionnaires were eligi-ble, and 8 had to be excluded due to missing signature or age <18 years. Of the included patients, 253 (62.6 %) were recruited by the dermatological university hospital in- and outpatient clinic and 151 (37.4 %) by private practices. The median age was 49 (18–85) years, and 54.5 % were male (Table 2).

Two hundred and four (50.5 %) of the psoriasis patients answered ≥4 questions with “yes”. Of these, 82 patients (40.2 %) stated to have known PsA (positive answer ques-tion 7) and filled out questionnaire 2. In 49/82 patients, the diagnosis was plausible according to questionnaire 2. Thirty-three (40.2 %) of the 82 patients who stated to have psoriatic arthritis were called by JCH, and the diagno-sis was interrogated. In 27/33 patients, the diagnosis was confirmed by an existing medical report (n = 17) or by an additional rheumatological examination at the university hospital Tuebingen (n = 10). In 4 patients, the diagnosis could not be confirmed.

Of those 122 patients with suspected PsA due to the number of positive questions and question 7 answered “no”, 24 (19.7 %) refused to come for a medical exami-nation and thus were counted as “absence of PsA”. In 10 patients (8.2 %), a medical report was available and 88 patients (71.1 %) were seen in our clinic for further evalua-tion of the presumed diagnosis.

Examined patients

The patient characteristics and the differentiation between new/confirmed PsA and absence of PsA of the 98 (88 patients with suspected PsA and 10 patients with possi-ble but questionable PsA) examined patients are depicted in Table 2. Fifty-two percent were male, and the median age was 50 (21–82) years. The median disease duration

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of psoriasis was 18.5 (1–57) years and the median age at the time of first skin manifestations was 30 (3–75.5) years. 61.2 % had a positive family history of psoriasis, and 59.2 % had psoriatic nail involvement. The patients reported of a median of 5 (0–43) years of arthralgia with a median age at first manifestation of 42.3 (10–74) years and an average of 5 (0–30) painful joints. A clinically evident or plausible history of dactylitis was significantly more common in patients with confirmed PsA (p = 0.023). In 11 patients, a spondyloarthritis (SpA) was suspected due to the reported answers in the questionnaire (especially questions 9–13).

In 45 patients (45.9 %), the diagnosis of PsA and in 5 patients (5.1 %) of SpA could be made by clinical and radi-ographic examinations. The median DAS28/44 or BASDAI of those patients was 3.04 (1.3–5.6)/1.97 (0.7–3.5) or 4.3 (0–8.2), respectively.

Regarding the laboratory parameters, the median CRP and ESR were 0.18 mg/dl (0.01–2.45) and 6 mm/h (0–57), respectively. Absence of rheumatoid factor and CCP anti-bodies was found in 96 and 95 % of the examined patients. HLA B27 was more often positive in patients with PsA/SpA than in patients without arthritis (12.2 vs. 2.2 %), but this did not reach significance (p = 0.113). The total num-ber of questions answered “yes” was significantly higher in the PsA group (9 vs. 7; p = 0.001). The severity of the skin manifestations was equally distributed among those with confirmed and those without PsA with only very few patients with very active skin disease at the time of pres-entation. In detail, 69.6 % of the patients with PsA and 69.1 % without PsA had no or mild skin activity (Table 3).

Of those patients where PsA could be ruled out by clinical work up (n = 48), we found osteoarthritis in 20 patients; symmetrical synovitis with anti-CCP antibod-ies and the diagnosis of rheumatoid arthritis in 2 patients; 4 patients suffered from fibromyalgia; 2 had gout; 2 had arthralgia due to traumatic reasons; and in 18 patients, no reason for the reported arthralgia could be found.

Twenty-two (22.5 %) of the examined patients were on systemic therapy for the skin manifestations with pos-sible influence also on the joint inflammation; 18 patients received methotrexate and 4 were on a TNF-antagonist. Only one of these patients was recruited by a private prac-tice; 21 were treated systemically by the dermatologic hospital.

Radiographic assessment (see Table 4)

In 94.9 % of the examined 98 patients, at least one imaging procedure was used to confirm the clinical suspicion. Ultra-sound with powerdoppler was performed in 82 patients (83.7 %) and detected inflammation typical of PsA in 46.3 %; whereas 13.4 % had typical signs of osteoarthritis, and in 40.2 %, no pathologic changes could be visualised. X-ray of hands and feet were available from 68 patients (69.4 %) and revealed characteristical alterations of PsA in 11.8 %, whereas arthrosis was diagnosed in 19.1 %.

MRI was used in 38 (38.3 %) patients. Of 11 patients with clinical suspicion of spinal involvement, spondyloar-thritis could be confirmed by MRI in 5 (45.5 %). Using MRI for peripheral joints in 20 patients (66.7 %), a typi-cal synovitis or tenosynovitis was confirmed, whereas in 10 patients (33.3 %), no pathological changes were found (Table 4).

In summary, in 282 patients (69.8 %), a PsA could be excluded, 78 patients (19.3 %) had known PsA, and in 44 patients (10.9 %), PsA/SpA was newly diagnosed by clini-cal rheumatological workup. This results in an overall prev-alence of PsA in patients with psoriasis of 30.2 % (Fig. 1).

Discussion

Prevalence of PsA in patients with psoriasis still shows a wide range even in recent studies. These discordant data may be explained by different evaluation methods and

Table 2 Analysis of all eligible questionnaires according to age, gender and place of recruitment. Patients were divided into patients recruited from the university hospital or private practices

Dermatologic hospital Dermatologic private practice Total

Number of patients 253 (62.6 %) 151 (37.4 %) 404 (100 %)

Gender

Male 137 (54.2 %) 83 (55 %) 220 (54.5 %)

Female 116 (45.8 %) 68 (45 %) 184 (45.5 %)

Median Age (range) in years 48 (18–85) 49 (18–84) 49 (18–85)

GePARD Questionnaire

Positive (≥4 questions answered “yes”) 139 (54.9 %) 65 (43.0 %) 204 (50.5 %)

Negative (<4 questions answered “yes”) 114 (45.1 %) 86 (57.0 %) 200 (49.5 %)

Median number of positive answers (range) 5 (0–14) 3 (0–13) 4 (0–14)

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diagnostic criteria used in the studies as well as by the specialisation of the recruiting and diagnosing physicians. Most work on prevalence of PsA in patients with psoria-sis was done by dermatologists. Regional and ethical dif-ferences also have an impact on the prevalence; especially, recent publications from Asia showed much lower rates of PsA than in Europe [4]. Even within Europe data are still variable. In the present study, we found a higher fre-quency than expected from two previous studies [1, 5] in Germany which revealed prevalences of 19 and 20.6 %, respectively. Radtke et al. [5] recruited patients from der-matologic practices using a standardised algorithm of questions, the Group for Research and Assessment of Pso-riasis and Psoriatic Arthritis (GRAPPA) criteria, but not a validated screening tool. No further diagnostic procedures

were performed in several patients with uncertain com-plaints. Reich et al. [1] recommended patients with psoria-sis from dermatological practices or outpatient clinics with the suspicion of arthritis to consult a rheumatologist. The diagnosis of PsA here was based on the Moll and Wright criteria, and patients with spine involvement were not included. Another recent study from the UK using database information of two large private practitioners to identify patients with psoriasis also referred to the CASPAR criteria for the diagnosis of PsA [7]. With a non-validated screen-ing questionnaire which was mailed to the patients and a clinical examination of those who agreed to come, the estimated prevalence was 13.8 %. A study from Italy from 2005 [8] found PsA in only 7.7 % of 923 patients who were hospitalised for moderate-to-severe psoriasis. Here, the

Table 3 Patient characteristics of those 98 patients who were clinically evaluated in Tuebingen with special regard to differences between those with and those without psoriatic arthritis. The PASI score was summarised to an activity score (AS) with the included PASI points given in ()

Psoriatic arthritis No psoriatic arthritis Significance

Number of patients (n = 98) 50 (51 %) 48 (49 %)

Gender

Male 26 (52.0 %) 25 (52.1 %) n.s.

Female 24 (48.0 %) 23 (47.9 %) n.s.

Median age (range) in years 50 (24–73) 48 (21–82) n.s.

Skin Psoriasis

Median disease duration 19.5 (1–56) 16 (1–57) n.s.

Median age at first manifestation 30.5 (3–65) 24 (6–75.5) n.s.

Positive family history for psoriasis 31 (62.0 %) 29 (60.4 %) n.s.

Positive psoriatic nail manifestations 31 (62.0 %) 27 (56.3 %) n.s.

Dactylitis

Positive question number 2 12 (24.0 %) 3 (6.3 %) p = 0.015

Laboratory

Median CRP (mg/dl) 0.21 (0.01–2.45) 0.17 (0.01–1.85) n.s.

Median ESR (mm/h) 6 (1–47) 5 (0–57) n.s.

Positive HLA-B27 6 (12.2 %) 1 (2.2 %) n.s. (p = 0.06)

PASI activity score

Not active (0–1 point) 11 (23.9 %) 11 (26.2 %) n.s.

Mild (2–10 points) 21 (45.7 %) 18 (42.9) n.s.

Moderate (11–15 points) 13 (28.3 %) 9 (21.4 %) n.s.

Median PASI AS (range) 1 (0–3) 1 (0–3) n.s.

DAS

Median DAS 28 (range) 3.04 (1.3–5.6) – –

Median DAS 44 (range) 1.97 (0.7–3.5) – –

Table 4 Radiographic findings of those 98 patients examined

Ultrasound/doppler X-ray MRI

Performed n (%) 82 (83.7) 68 (69.4) 38 (39.8)

Pathologic

Typical PsA n (%) 38 (46.3) 8 (11.8) 20 (66.7)

Osteoarthritis (%) 11 (13.4) 13 (19.1) 3 (10)

Spondylitis n (%) – – 5 (62.5)

No inflammation/no PsA/no osteoarthritis (%) 33 (40.2) 47 (69.1) 10 (33.3)

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European Spondyloarthropathy Study Group (ESSG) crite-ria were used by the dermatologists. Only a registry study with the highest number of participants from Scandinavia published by Zachariae [6] in 2002 described a comparable prevalence rate with 30 % in 5795 patients with psoriasis.

Different validated screening tools were published during the last years. The psoriatic arthritis screening and evalua-tion (PASE) Questionnaire is a 15 item questionnaire with a sensitivity and specificity of 76 % in a cohort of 190 patients [20] and a score cut-off of 44 (the score ranges 0–75). A cut-off of 47 was able to detect PsA with 82 % sensitivity and 73 % specificity in a second trial [21]. The Toronto Psoriatic Arthritis Screening (ToPAS) Questionnaire was developed as a screening tool for PsA in patients with psoriasis as well as in the general population [22] and was validated in differ-ent patient groups with a sensitivity and specificity of 86.8 and 93.1 %. It includes pictures of skin and nail manifesta-tions of psoriasis. PASE and ToPAS as well as the psoria-sis epidemiology screening tool (PEST), which is a simple 5 question screening, include a stick figure to mark painful joints. It has shown a sensitivity of 94 % and a specificity of 78 % [23] and were compared recently with good results for both questionnaires and a slight advantage for ToPAS and PEST [24]. We decided for the GEPARD Questionnaire as it is the only validated questionnaire in German language and very easy to perform and analyse.

This is the first study on prevalence of PsA in patients with psoriasis in Germany using the validated GEPARD Questionnaire. We used a combination of a standardised

physical rheumatological examination, laboratory and the validated CASPAR criteria for diagnosis. Patients were recruited consecutively by dermatologists which improves the certainty on the diagnosis of psoriasis. The evaluation of the questionnaires as well as the diagnosis of PsA was performed by rheumatologists. All eligible patients were examined by the same rheumatologist. Those patients who stated to already have the diagnosis of psoriatic arthritis were interrogated through the telephone. In more than 1/3 of patients MRI, as a very sensitive and specific imaging method, was performed in addition to the powerdoppler examination or X-ray, which were available in 84 and 63 % of the patients, respectively. Hence, certainty of the diagno-sis of arthritis is very high.

A screening method for dermatologists to identify patients at risk for PsA is of great value for the patient, in order to diagnose and treat PsA as early as possible and consecutively prevent damage. However, this pre-screening still is not fully satisfying for the rheumatologists as too many (>60 %) wrongly positive questionnaires occurred, supporting the findings from other groups who found arthralgia in many patients with psoriasis without arthri-tis [8, 25]. To optimise the preselection, we analysed the use of serum inflammatory markers, but neither CRP nor ESR or even HLA B27 could significantly improve the dis-crimination between arthritis and arthralgia. Similarly, the severity of skin psoriasis or presence of nail involvement did not appear to be helpful. Other studies confirmed the missing correlation of severity of skin manifestations and

Fig. 1 Simplified flowchart of patients. Patients who answered ≥4 questions “yes” were invited for further examinations

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the occurrence of PsA [8, 26]. Thus, adding serum inflam-matory markers or any skin severity rating to the question-naire does not improve its quality. Regarding the questions separately, only the history of self-reported dactylitis and of known psoriatic arthritis (questions 2 + 7) was signifi-cantly associated with the finally confirmed diagnosis of PsA. Putting more weight on these two questions could improve the specificity of the questionnaire. An important issue for question 7 could be a further question about the diagnosis being made by a rheumatologist.

This study has some limitations. The sample size is still small to determine an exact prevalence rate. As psoriasis is a very common disease with more than 2,000,000 patients in Germany, we only included 0.02 % of them. More than 60 % of patients were recruited by the dermatological uni-versity hospital, and thus, the prevalence rate might be biased by the more severe cases seen at the hospital. When dividing into patients from dermatologic hospital and pri-vate practice, more patients from the hospital had PsA (22.8 vs. 7.4 %) although patients from private practices had more often moderate-to-severe skin manifestations (29.1 vs. 8.6 %). This might be explained by a higher num-ber of patients treated systemically for their skin manifesta-tions in the participants recruited by the hospital. On the other hand, all patients who refused to be examined by a rheumatologist and the 2 patients with rheumatoid arthri-tis were included in the prevalence calculation and were counted negative for PsA. Thus, the exact prevalence of PsA may be even higher than calculated here.

In summary with 19 % known and 11 % new diagnosed PsA, the prevalence of PsA among patients with psoriasis is high (30 %) and all physicians and especially the der-matologists should be aware of the risk for their patients. The GEPARD or similar questionnaires can be of great advantage for patients as the pre-screening is simple and inexpensive for the dermatologists, and an early referral to a rheumatologist may avoid joint destruction as PsA can be treated very effectively today.

Acknowledgments We also thank Dr. R. Denfeld, Dr. A. Philipp, Dr. P. Ziegler and Dr. M. Kleinhans who also recruited patients for this study, but did not meet the criteria for authorship. This study was supported by an unrestricted grant from Pfizer. The company had no influence on the study protocol, data analysis or conclusions.

Conflict of interest The authors declare that they have no compet-ing interests.

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