ARTHRITIS & RHEUMATISMVol. 64, No. 10, October 2012, pp 3150–3155DOI 10.1002/art.34536© 2012, American College of Rheumatology

Sensitivity and Specificity of the Classification ofPsoriatic Arthritis Criteria in Early Psoriatic Arthritis

Laura C. Coates,1 Philip G. Conaghan,1 Paul Emery,1 Michael J. Green,2

Gamal Ibrahim,3 Helen MacIver,3 and Philip S. Helliwell1

Objective. To assess the sensitivity and specificityof the Classification of Psoriatic Arthritis (CASPAR)Study Group criteria in early psoriatic arthritis (PsA)and to compare them with the sensitivity and specificityof the Moll and Wright criteria.

Methods. The CASPAR Study Group criteria wereapplied to patients with early PsA (<24 months symp-tom duration) and to control patients with other new-onset inflammatory arthritides. Both groups were naiveto all disease-modifying antirheumatic drugs. The goldstandard diagnosis was confirmed by the consultingrheumatologist using radiography and magnetic reso-nance imaging where required. Proportions of patientsand control patients meeting the criteria were comparedusing McNemar’s tests.

Results. We recruited a total of 111 patients withearly PsA and 111 control patients with other forms ofinflammatory arthritis (82 with rheumatoid arthritis, 13with undifferentiated arthritis, 9 with spondylarthritis,4 with inflammatory osteoarthritis, and 3 with crystalarthritis) to the study. The sensitivity of the CASPAR

Study Group criteria in classifying early PsA was 87.4%compared to 80.2% for the Moll and Wright criteria.The specificity for both criteria was 99.1%. When con-sidering different cut points for the CASPAR StudyGroup criteria, the best cut point for classificationremained a score of >3 as in the original CASPARStudy Group analysis. Considering a score of >2 gave ahigher sensitivity of 99.1% but resulted in a drop inspecificity to 94.6%. Regression analysis determinedthat psoriasis and rheumatoid factor negativity werethe most important features that differentiated PsA,followed by nail psoriasis and current or previousdactylitis.

Conclusion. The CASPAR Study Group criteriaare more sensitive than the Moll and Wright criteria inclassifying early PsA. Although their sensitivity for earlyPsA is lower than that for established disease, theCASPAR Study Group criteria are valid for use asinclusion criteria for trials in early PsA.

The Classification of Psoriatic Arthritis (CASPAR)Study Group criteria were developed as new classifica-tion criteria for psoriatic arthritis (PsA) using a largecohort of patients with PsA and controls with otherinflammatory arthritides. They include characteristicfeatures of PsA and have been shown to have highsensitivity and specificity in a population with estab-lished disease (1). However, one of the limitations of theCASPAR Study Group criteria is that they have notbeen validated in early disease. A retrospective survey ofthe Toronto database found that the CASPAR StudyGroup criteria had high sensitivity for identifying earlydisease within their PsA clinic population (2). However,that study included only patients referred to a specialisttertiary referral clinic; therefore, there is a significantrisk of overestimating the sensitivity of the criteria.Studies in Italy and Sweden have also investigated the

Dr. Coates was recipient of a Clinical Research Fellowshipfrom Arthritis Research UK (grant number 18364).

1Laura C. Coates, MBChB, PhD, MRCP, Philip G.Conaghan, MBBS, PhD, FRCP, FRACP, Paul Emery, MA, MD,FRCP, Philip S. Helliwell, MA, DM, PhD: University of Leeds andNIHR Leeds Musculoskeletal Biomedical Research Unit, Leeds, UK;2Michael J. Green, MBChB, MRCP: York Teaching Hospital NHSFoundation Trust, York, and Harrogate and District NHS FoundationTrust, Harrowgate, UK; 3Gamal Ibrahim, ABMS, MSc, FRCP, HelenMacIver, MBChB, MRCP: St. Luke’s Hospital and Bradford TeachingHospital NHS Foundation Trust, Bradford, UK.

Dr. Emery has received consulting fees, speaking fees, and/orhonoraria from Pfizer, MSD, Abbott, Roche, UCB, Celgene, andBristol-Myers Squibb (less than $10,000 each).

Address correspondence to Philip S. Helliwell, DM, PhD,Division of Musculoskeletal and Rheumatic Diseases, Chapel AllertonHospital, Chapeltown Road, Leeds LS7 4SA, UK. E-mail:p.helliwell@leeds.ac.uk.

Submitted for publication July 15, 2011; accepted in revisedform May 3, 2012.

3150

sensitivity of the criteria in early PsA (3,4), but as yet nostudies have been completed with a control populationto address the sensitivity and specificity of the CASPARStudy Group criteria in early disease. The criteria cannotcurrently be recommended for use in studies of earlyPsA.

The other key issue raised with the CASPARStudy Group criteria is the entry criterion that statesthat the patients must have “inflammatory articulardisease (joint, spine, or entheseal).” Particularly in earlyPsA, the pattern of disease may be evolving and may bedifferent from that of established disease.

This study aimed to emulate the methodology ofthe original CASPAR study and to recruit both patientswith early PsA and control patients with other inflam-matory arthritides to allow calculation of the sensitivityand specificity of the criteria in this population ofpatients with early PsA. The Moll and Wright criteria,which state that patients have PsA if they have inflam-matory arthritis, psoriasis, and (usually) are negative forrheumatoid factor (RF) (5), were used for compar-ison. In addition, an assessment of arthritis, enthesitis,and axial involvement was included to investigate thepattern of disease in treatment-naive patients with earlyarthritis.

PATIENTS AND METHODS

Patient and control selection. Patients and controlswere recruited from Early Arthritis Clinics and from newreferrals to rheumatology clinics in 4 hospitals based in theYorkshire region. Consecutive clinic attendees newly diag-nosed as having PsA were enrolled in the study. All PsApatients were required to have active inflammatory musculo-skeletal disease comprising arthritis and/or enthesitis and/ordactylitis. For each patient enrolled, a consecutive controlpatient with new-onset inflammatory musculoskeletal diseasewas also enrolled. The gold standard diagnosis was confirmedby the consulting rheumatologist using radiography and mag-netic resonance imaging (MRI) where required. All patientsand controls were required to have disease duration of �2years (from onset of symptoms) and to be disease-modifyingantirheumatic drug naive.

Data collection. Data were recorded on standardizedforms that included demographics, date of onset of arthritis,duration of early morning stiffness, activity of arthritis/enthesitis and axial disease, and application of the CASPARStudy Group criteria. Activity of arthritis and enthesitis wasassessed using clinical examination. All patients underwent aswollen joint count (66 joints), a tender joint count (68 joints),and clinical assessment of entheses, including the enthesealsites required for the Leeds Enthesitis Index (6), the Maas-tricht Ankylosing Spondylitis Enthesitis Score (MASES) (7),and sites used in the Infliximab Multinational Psoriatic Arthri-

tis Controlled Trial (IMPACT) and IMPACT 2 clinical trials(bilateral Achilles tendon and plantar fascia) (8,9). Entheseswere considered to have active enthesitis if they were tenderand/or swollen. The presence of axial involvement was assessedclinically by questioning the patient about inflammatory backpain using the Calin criteria (10).

All patients underwent plain radiography of the handsand feet and additional imaging as deemed clinically necessaryby the treating physician. Patients with symptoms suggestive ofinflammatory back pain underwent radiography and MRI asclinically indicated. Results of all relevant investigations wererecorded, including levels of inflammatory markers, IgM-RFand anti–cyclic citrullinated peptide antibodies, presence orabsence of typical PsA-like periosteal new bone formation onradiographs, and evidence of axial involvement identified withradiographs or MRI by consensus of radiologists and thereferring rheumatologist in each center (11).

When considering patterns of arthritis, oligoarthritiswas defined as �5 joints with active disease and polyarthritis as�5 joints with active disease. Small joints were defined astemporomandibular joints, sternoclavicular joints, acromiocla-vicular joints, carpometacarpal joints, metacarpal joints, prox-imal and distal interphalangeal (DIP) joints, metatarsophalan-geal joints, and interphalangeal joints of the toes (total of 58joints). Large joints were defined as the glenohumeral joints,elbows, hips, knees, and ankle joints (total of 10 joints). Thesymmetry number was calculated as the number of joints assymmetric pairs/total number of joints involved. Symmetrywas defined as a symmetry number of �0.5 as previouslydescribed (12).

Statistical analysis. Values for sensitivity and specific-ity for the CASPAR Study Group criteria in establisheddisease are 0.91 and 0.99, respectively. Prior to the develop-ment of the CASPAR Study Group criteria, the Moll andWright criteria were traditionally used, and the values forsensitivity and specificity for the Moll and Wright criteria inthe CASPAR study were 0.99 and 0.92, respectively. Assumingthat in early case definition the emphasis is on specificity, thenull hypothesis is that the specificity for the CASPAR StudyGroup criteria will be equivalent to that for the Moll andWright criteria (HA � HO, respectively). The alternativehypothesis is that the specificity for the CASPAR Study Groupcriteria differs from that for the Moll and Wright criteria(HA � HO). According to Obuchowski (13), the number ofpatients required to test the alternative (2-tailed) hypothesiswith an alpha value of 0.05 and a beta value of 0.20 is 111.Therefore, 111 patients and 111 consecutive control patientswere required.

Sensitivity and specificity of the CASPAR StudyGroup criteria and Moll and Wright criteria were comparedusing McNemar’s tests for paired variables. Receiver operatingcharacteristic (ROC) curves were used to estimate the areaunder the curve (AUC) for both criteria and the optimal cutpoint for the CASPAR Study Group criteria for the diagnosisof early PsA. Univariate and multivariate forward stepwisebinary logistic regression was used to identify which featuresincluded in the CASPAR Study Group criteria were indepen-dently associated with PsA. Significance testing was performed

USE OF CASPAR CRITERIA IN EARLY PsA 3151

using McNemar’s tests for categorical variables and Mann-Whitney U tests for continuous variables.

RESULTS

We recruited a total of 111 patients with earlyPsA and 111 control patients with other forms ofinflammatory arthritis (82 with rheumatoid arthritis[RA], 13 with undifferentiated arthritis, 9 with spondy-larthritis, 4 with inflammatory osteoarthritis, and 3 withcrystal arthritis) to the study. The baseline features ofthese patients are shown in Table 1. The sensitivity ofthe CASPAR Study Group criteria (score �3) in classi-fying early PsA was 87.4% compared to 80.2% for theMoll and Wright criteria (P � 0.008). The specificity forboth criteria was 99.1%, with only 1 control patientfulfilling both criteria for PsA.

Using ROC analysis, the AUC for the CASPARStudy Group criteria was 0.991 compared to 0.896 forthe Moll and Wright criteria (Figure 1). When consid-ering different cut points for the CASPAR Study Groupcriteria, the best cut point for classification remained a

score of �3 as in the original CASPAR Study Groupanalysis (Table 2). Considering a score of �2 gave ahigher sensitivity but resulted in a drop in specificity thatwould not be ideal for classification criteria.

When considering the individual components ofthe CASPAR Study Group criteria, 96.4% of PsApatients had current or previous psoriasis or a familyhistory of psoriasis with 84% having current psoriasis.Dactylitis and nail psoriasis were highly discriminatory,as only 1 control patient each had these features.Univariate binary logistic regression analysis determinedthat all of the features of the CASPAR Study Groupcriteria, with the exception of radiographic evidence ofnew bone formation, were significant in distinguishing

Table 1. Baseline features of the PsA patients and control patientsrecruited to the CASPAR study*

PsApatients

(n � 111)

Controlpatients

(n � 111)

Age, median (IQR) years 44 (34–55) 52 (38–66)Disease duration, median (IQR) months 8 (5–14) 5 (3–9.25)Consultant diagnosis, no. of patients

PsA 111 0RA 0 82UA 0 13SpA 0 9

ReA 0 6IBD related 0 2Axial SpA 0 1

Inflammatory OA 0 4Crystal arthritis 0 3

Arthritis, % 100 99Enthesitis, % 67† 52Axial symptoms, % 5 1Early morning stiffness, median (IQR)

minutes60 (20–120) 60 (30–120)

Fulfilling Moll and Wright criteria forPsA, %

80† 1

Fulfilling CASPAR Study Group criteriafor PsA, %

87† 1

* PsA � psoriatic arthritis; CASPAR � Classification of Psoriatic Ar-thritis; IQR � interquartile range; RA � rheumatoid arthritis;UA � undifferentiated arthritis; SpA � spondylarthritis; ReA � reac-tive arthritis; IBD � inflammatory bowel disease; OA � osteoarthri-tis.† P � 0.05 versus control patients.

Figure 1. Receiver operating characteristic curve for the Classifica-tion of Psoriatic Arthritis (CASPAR) Study Group criteria and theMoll and Wright criteria predicting psoriatic arthritis diagnosis.

Table 2. Receiver operating characteristic curve analysis of the Molland Wright criteria and the CASPAR Study Group criteria*

Criteria Score Sensitivity Specificity

Moll and Wright Positive 80.2 99.1CASPAR Study Group

criteria score�1 100 42.3�2 99.1 94.6�3 87.4 99.1�4 42.3 100�5 15.3 100

* CASPAR � Classification of Psoriatic Arthritis.

3152 COATES ET AL

PsA patients from control patients. Multivariate forwardstepwise logistic regression determined that current orprevious psoriasis, RF negativity, nail psoriasis, familyhistory of psoriasis, and current or previous dactylitiswere all associated with PsA. Table 3 shows in moredetail the proportion of patients fulfilling each individ-ual aspect of the CASPAR Study Group criteria.

When considering the diagnosis of inflammatoryarticular disease (joint, spine, or entheseal) required forthe first aspect of the CASPAR Study Group criteria,there were some minor differences between the PsApatients and control patients. Nearly all patients hadarthritis. Enthesitis was significantly more frequent inPsA patients than in control patients (67% versus 52%;

P � 0.029). There was a trend toward higher enthesitiscounts in PsA patients compared to control patients, butthis was not significant. When considering the 3 clinicalindices for enthesitis (MASES, Leeds Enthesitis Index,and IMPACT) individually, there was again a trendtoward higher enthesitis scores in PsA patients com-pared to control patients, but this was only significantwhen using the IMPACT tool (P � 0.022). There wereno individual entheseal sites or other combinations ofentheseal sites that could distinguish PsA patients fromcontrol patients. Spondylitis appeared more frequentlyin PsA patients, but the difference was not significantdue to small numbers (5% versus 1%; P � 0.055).

Further analysis examined the pattern of arthritisseen in PsA patients and patients with other inflamma-tory arthritides (Table 4). The average tender andswollen joint counts and the proportions of people witholigoarticular and polyarticular disease did not differsignificantly between PsA patients and control patients.Involvement of large and small joints was also similarwhen comparing PsA patients to all control patients.The 82 control patients with RA were found to havesignificantly higher joint counts (P � 0.008), principallydue to an increased number of small joints involved.More than 60% of RA patients had predominantly smalljoint disease. However, DIP joint involvement was sig-nificantly more common in PsA patients than in allcontrol patients (32% versus 16%; P � 0.007) and more

Table 3. Proportion of PsA patients and control patients fulfillingeach aspect of the CASPAR Study Group criteria*

PsApatients

(n � 111)

Controlpatients

(n � 111)

Any psoriasis 96† 12Current psoriasis 84† 4Previous psoriasis 6† 1Family history of psoriasis 18† 8

Nail psoriasis 38† 1Rheumatoid factor negative 96† 47Current or previous dactylitis 28† 1Radiographic evidence of new bone formation 2 0

* Values are the percent of patients. See Table 1 for definitions.† P � 0.05 versus control patients.

Table 4. Disease patterns in PsA patients, all patient controls, and RA patient controls*

PsA patients(n � 111)

All patient controls(n � 111)

RA patient controls(n � 82)

Proportion with arthritis, % 100 99 100Oligoarthritis, % 30 24 15Polyarthritis, % 70 76 85DIP joint involvement, no. (%) 35 (32)†‡ 18 (16) 15 (18)Tender joint count, median (IQR) 7 (3–16)‡ 8 (4–19) 12 (6–22)Swollen joint count, median (IQR) 5 (2–9)‡ 5 (3–12) 7 (3–14)Joints with active disease, median (IQR) 9 (4–17)‡ 10 (5–20) 12.5 (7–23)Predominantly small joint arthritis, no. (%) 59 (54) 59 (54) 50 (62)Predominantly large joint arthritis, no. (%) 51 (46) 50 (45) 31 (38)Small joints involved, median (% of total) 7 (12)‡ 9 (16) 11.5 (20)Large joints involved, median (% of total) 1 (10) 1 (10) 1.5 (15)Symmetry number, median (IQR) 0.5 (0–0.78)†‡ 0.67 (0.29–0.86) 0.73 (0.49–0.89)Symmetric disease, no. (%) 58 (52)‡ 72 (65) 62 (76)

Proportion with enthesitis, % 67† 52 52Enthesitis count, median (IQR) 2 (0–4) 1 (0–3) 1 (0–4)

Proportion with spondylitis, % 5 1 0

* DIP � distal interphalangeal (see Table 1 for other definitions).† P � 0.05 versus all control patients.‡ P � 0.05 versus RA control patients.

USE OF CASPAR CRITERIA IN EARLY PsA 3153

common in PsA patients than in RA patients alone(18%).

It has been suggested that a symmetry number of�0.5 defines symmetric disease (12). The symmetrynumber was significantly higher in all control patientsthan in PsA patients (P � 0.003), and this difference waseven more pronounced when comparing RA controlpatients with PsA patients (P � 0.0001). The remainingcontrol patients (without RA) had a lower mediansymmetry number, but this was not significant whencompared to PsA patients (0.27 versus 0.5; P � 0.58). Ahigher proportion of control patients, particularly thosewith RA, had symmetric disease compared to PsApatients. When we compared PsA patients to all controlpatients, there was no significant difference in theproportion with symmetric disease (P � 0.11); however,there was a significant difference when we comparedPsA patients to RA control patients (P � 0.001).

DISCUSSION

These data confirm that the CASPAR StudyGroup criteria have greater sensitivity than the Moll andWright criteria in the identification of early PsA. Themost important difference between the 2 criteria is thatthe CASPAR Study Group criteria allow a diagnosis ofPsA to be made in patients without skin psoriasis. TheCASPAR Study Group criteria use additional featuressuch as dactylitis, nail psoriasis, and positive familyhistory to increase their sensitivity. This is particularlyrelevant in early disease, when not all features of PsAmay have become manifest. In particular, 20% of peoplepresenting with PsA do not have skin psoriasis, therebyexcluding them from a diagnosis using the Moll andWright criteria. All RF-negative patients who fulfill theMoll and Wright criteria will also fulfill the CASPARStudy Group criteria, so there is significant overlapbetween the 2 sets of criteria.

In comparison with their sensitivity for detectingestablished disease, the sensitivity of the CASPARcriteria remains slightly lower for detecting early PsA. Ashort duration of disease means that many patients willnot yet have experienced all of the typical features ofPsA that they may develop during the course of theirdisease. In particular, there is a much lower incidence oftypical radiographic changes that can be identified inpatients with early PsA. The vast majority of patientswith new onset of inflammatory arthritis have normal-appearing radiographs at presentation. This problemhas been identified in previous cohorts of patients with

early PsA, in whom little new bone formation could beidentified (3).

When considering the pattern of inflammatoryarticular disease, a higher proportion of PsA patientshad enthesitis compared to control patients. Most of theclinical indices and clinical examinations of individualenthesis sites were not able to discriminate between PsApatients and control patients. It is known that clinicalassessment for tenderness near an enthesis correlatespoorly with ultrasound or MRI in identifying enthesitis.Therefore, this may reflect a failure of the clinicalentheseal indices rather than a similar picture of enthesi-tis in the PsA patients and control patients. More PsApatients had axial disease, although this difference wasnot significant due to small numbers affected in bothgroups. Patterns of arthritis showed that PsA patientshad a lower total number of involved joints compared toRA control patients, and this difference was principallyexplained by a higher number of involved small joints inRA patients, confirming the identification of RA as apredominantly small joint polyarthropathy. Symmetricjoint disease was less common in PsA patients than inRA control patients, and there was a significant differ-ence in symmetry number between PsA patients and allcontrol patients.

The most significant limitation of this study re-lates to the selection of the PsA patients. PsA patientswere recruited only if they were diagnosed by an expe-rienced rheumatologist as having PsA, and few patientspresenting with undifferentiated arthritis were includedin this study. This may be less important when consid-ering the use of the CASPAR Study Group criteria asclassification criteria for enrollment in clinical trials, asoriginally intended. The results of this study supporttheir use as inclusion criteria for future research studiesof recent-onset PsA. However, these data will result inan overestimate of the sensitivity of the criteria if theiruse is considered as a diagnostic or screening tool in ageneral Early Arthritis Clinic population. Nearly all ofthe patients and controls recruited into this study hadactive arthritis, although this was not a mandatoryinclusion criterion. Patients presenting with isolatedenthesitis or dactylitis are less common and may have adelay in diagnosis that would have excluded them fromparticipation in this study. The other limitation is theidentification of ideal controls. Again, controls are morelikely to have a certain diagnosis, such as RA, andpatients with undifferentiated arthritis were not seen insignificant numbers. It is also difficult to identify a sig-

3154 COATES ET AL

nificant number of controls presenting with axial spon-dylarthritis who have �2 years of symptom duration.

This work supports the use of the CASPARStudy Group criteria as classification criteria for futureresearch in early PsA. Although the sensitivity of thesecriteria is slightly lower than that in established disease,the specificity is reassuring. Their use as diagnosticcriteria in cases where diagnosis is unclear cannot berecommended based on this study, but future workevaluating their use in an unselected Early ArthritisClinic population would address this issue. A differentclinical phenotype cannot be relied upon in isolation toidentify early PsA, but different patterns are seen in PsApatients compared to patients with other inflammatoryarthritides. Enthesitis and DIP joint involvement aremore frequent in early PsA compared to other forms ofinflammatory arthritis; however, a significant proportionof controls (including a significant proportion of patientswith RA) also have clinical enthesitis. Spondylitis islikely to be more frequent in PsA than in RA; however,it cannot be relied upon to differentiate PsA from otherforms of inflammatory arthritis. Patterns of arthritisconfirm the typical view that RA is a symmetric predom-inantly small joint polyarthropathy, whereas patientswith PsA generally present with fewer involved joints,particularly fewer involved small joints, and with lesssymmetric disease.

AUTHOR CONTRIBUTIONS

All authors were involved in drafting the article or revising itcritically for important intellectual content, and all authors approvedthe final version to be published. Dr. Helliwell had full access to all ofthe data in the study and takes responsibility for the integrity of thedata and the accuracy of the data analysis.Study conception and design. Coates, Helliwell.Acquisition of data. Coates, Conaghan, Green, Ibrahim, MacIver,Helliwell.Analysis and interpretation of data. Coates, Conaghan, Emery,Helliwell.

REFERENCES

1. Taylor W, Gladman D, Helliwell P, Marchesoni A, Mease P,Mielants H, and the CASPAR Study Group. Classification criteriafor psoriatic arthritis: development of new criteria from a largeinternational study. Arthritis Rheum 2006;54:2665–73.

2. Chandran V, Schentag CT, Gladman DD. Sensitivity of theclassification of psoriatic arthritis criteria in early psoriatic arthri-tis. Arthritis Rheum 2007;57:1560–3.

3. D’Angelo S, Mennillo GA, Cutro MS, Leccese P, Nigro A, PadulaA, et al. Sensitivity of the classification of psoriatic arthritis criteriain early psoriatic arthritis. J Rheumatol 2009;36:368–70.

4. Lindqvist UR, Alenius GM, Husmark T, Theander E, HolmstromG, Larsson PT. The Swedish early psoriatic arthritis register—2-year followup: a comparison with early rheumatoid arthritis.J Rheumatol 2008;35:668–73.

5. Moll JM, Wright V. Psoriatic arthritis. Semin Arthritis Rheum1973;3:55–78.

6. Healy PJ, Helliwell PS. Measuring clinical enthesitis in psoriaticarthritis: assessment of existing measures and development of aninstrument specific to psoriatic arthritis. Arthritis Rheum 2008;59:686–91.

7. Heuft-Dorenbosch L, Spoorenberg A, van Tubergen A, LandeweR, van ver Tempel H, Mielants H, et al. Assessment of enthesitisin ankylosing spondylitis. Ann Rheum Dis 2003;62:127–32.

8. Antoni C, Krueger GG, de Vlam K, Birbara C, Beutler A, GuzzoC, et al. Infliximab improves signs and symptoms of psoriaticarthritis: results of the IMPACT 2 trial. Ann Rheum Dis 2005;64:1150–7.

9. Antoni CE, Kavanaugh A, Kirkham B, Tutuncu Z, Burmester GR,Schneider U, et al. Sustained benefits of infliximab therapy fordermatologic and articular manifestations of psoriatic arthritis:results from the Infliximab Multinational Psoriatic Arthritis Con-trolled Trial (IMPACT) [published erratum appears in ArthritisRheum 2005;52:2951]. Arthritis Rheum 2005;52:1227–36.

10. Calin A, Porta J, Fries JF, Schurman DJ. Clinical history as ascreening test for ankylosing spondylitis. JAMA 1977;237:2613–4.

11. Rudwaleit M, Jurik AG, Hermann KG, Landewe R, van derHeijde D, Baraliakos X, et al. Defining active sacroiliitis onmagnetic resonance imaging (MRI) for classification of axialspondyloarthritis: a consensual approach by the ASAS/OMER-ACT MRI group. Ann Rheum Dis 2009;68:1520–7.

12. Helliwell PS, Hetthen J, Sokoll K, Green M, Marchesoni A,Lubrano E, et al. Joint symmetry in early and late rheumatoid andpsoriatic arthritis: comparison with a mathematical model. Arthri-tis Rheum 2000;43:865–71.

13. Obuchowski NA. Sample size calculations in studies of testaccuracy. Stat Methods Med Res 1998;7:371–92.

USE OF CASPAR CRITERIA IN EARLY PsA 3155