Sensitivity of the Classification of PsoriaticArthritis Criteria in Early Psoriatic ArthritisVINOD CHANDRAN, CATHERINE T. SCHENTAG, AND DAFNA D. GLADMAN

Introduction

Psoriatic arthritis (PsA) is defined as an inflammatory ar-thritis associated with cutaneous psoriasis, usually sero-negative for rheumatoid factor (RF) (1). The clinical pre-sentation of PsA varies. Patients have a peripheral arthritis(oligoarthritis or polyarthritis), enthesitis, dactylitis, sac-roiliitis, and spondylitis, occurring alone or in combina-tion (1). Epidemiologic and genetic research in PsA hasbeen hampered by the lack of validated or widely agreedupon classification criteria for PsA. Although a number ofclassification criteria have been proposed (2), none havebeen widely agreed upon or validated (3). Recently, theClassification of Psoriatic Arthritis (CASPAR) StudyGroup published new criteria for the classification of PsAthat were derived from a data set of 588 patients with PsAand 536 controls with other inflammatory arthritis (2). Thesensitivity and specificity of the CASPAR criteria in theoriginal study were 91.4% and 98.7%, respectively (2).However, patients with PsA had longstanding disease witha mean disease duration of 12.5 years. It was thereforerecommended that the criteria be tested in early PsA. Theconcept of early PsA is new and there have not been manystudies on early PsA. The definition of early PsA has beenextrapolated from early rheumatoid arthritis, and the usualdefinition is inflammatory arthritis associated with psori-asis, usually negative for RF with disease duration �2years (4,5), although studies have used varying cutoffs(6,7). The objective of the present study was to determinethe sensitivity of the CASPAR criteria in patients withearly PsA.

Patients and Methods

The study was conducted at the University of TorontoPsoriatic Arthritis clinic where a well-characterized, open,dynamic cohort of patients with PsA has been establishedsince 1978. Patients were evaluated using a standard pro-tocol at the first visit and subsequently every 6–12 months.A detailed description of the protocol has been previouslyreported (8). Some of the key definitions in the protocolwere as follows: Actively inflamed joints were defined asthe number of joints with tenderness and/or swelling(based on 68 joints tested for tenderness, and 66 for swell-ing) (9). Swollen joint count was defined as the number ofjoints with swelling, not due to bony overgrowth. Clini-cally damaged joint count was defined as the number ofjoints with either limited movement �20% of the normalrange, not due to effusion, including subluxation and flex-ion contracture; ankylosis; flail joint; and surgery. Radio-graphic damage to peripheral joints was recorded usingthe modified Steinbrocker method (10). The scores indi-cated the number of joints (out of 42 assessed) with at least1 erosion. In addition, periosteal reaction and juxtaarticu-lar new bone formation, pencil-in-cup change, tuft resorp-tion, enthesitis, spur formation, presence of sacroiliitis(New York criteria [11]), and syndesmophytes were re-corded. Psoriasis was assessed by the Psoriasis Area andSeverity Index (PASI) (12). Methods used in the clinichave been found to be reliable (9,13).

All items included in the CASPAR criteria, namely,presence of inflammatory articular disease, current psori-asis, personal history of psoriasis, family history of psori-asis, psoriatic nail dystrophy, presence of current dactyl-itis, and history of dactylitis, were recorded at each visitand tracked on a computerized database. Patients weretested for RF at the first visit and yearly thereafter. Radio-graphic evidence of juxtaarticular new bone formation wasrecorded at the first visit and every 2 years thereafter.

Patients with PsA who enrolled in the clinic betweenJuly 1990 and October 2004 were included in the presentstudy. The gold standard was a diagnosis of PsA by anexperienced rheumatologist (DDG). Those enrolled priorto July 1990 were excluded because prior to that date RFwas tested by latex agglutination. The CASPAR criteriarequire that RF be tested by any method except latexagglutination, preferably enzyme-linked immunosorbent

Supported in part by the Krembil Foundation. Dr. Chan-dran’s work was supported by the Krembil Psoriatic Arthri-tis Fellowship.

Vinod Chandran, MBBS, MD, DM, Catherine T. Schentag,MSc, Dafna D. Gladman, MD, FRCPC: Centre for PrognosisStudies in the Rheumatic Diseases, Toronto Western Hospi-tal, Toronto, Ontario, Canada.

Address correspondence to Dafna D. Gladman, MD,FRCPC, Toronto Western Hospital, 399 Bathurst Street1E-410B, Toronto, Ontario M5T 2S8, Canada. E-mail:dafna.gladman@utoronto.ca.

Submitted for publication March 14, 2007; accepted inrevised form May 29, 2007.

Arthritis & Rheumatism (Arthritis Care & Research)Vol. 57, No. 8, December 15, 2007, pp 1560–1563DOI 10.1002/art.23104© 2007, American College of Rheumatology

CONTRIBUTIONS FROM THE FIELD

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assay or nephelometry (2). In those patients included, RFwas tested by nephelometry. Patients were arbitrarily di-vided into 2 groups at the first clinic visit: those with earlyPsA (defined as disease duration �2.5 years) and thosewith late PsA (defined as disease duration �2.5 years).CASPAR criteria were applied at the time of the first visitto the clinic in both groups. To satisfy the CASPAR crite-ria, a patient had to have inflammatory articular disease(joint, spine, or entheseal) with at least 3 points from thefollowing features: current psoriasis (assigned a score of 2;all other features were assigned a score of 1), a history ofpsoriasis (unless current psoriasis was present), a familyhistory of psoriasis in a first- or second-degree relative(unless current psoriasis was present or there was a historyof psoriasis), dactylitis, juxtaarticular new bone formation,RF negativity, and nail dystrophy (2).

Descriptive statistics are provided. Sensitivity was cal-culated on the basis of the number of patients satisfyingcriteria and confidence intervals were calculated.

ResultsThe demographic and disease characteristics of the pa-tients included in this study are given in Table 1. Pa-tients with early disease had an average disease durationof 1 year. Those with late disease had an average diseaseduration of 11 years, which was comparable with that ofthe original CASPAR study (2). As expected, patients withearly PsA had lower clinical and radiographic damage.The actively inflamed joint counts and PASI score werecomparable.

The sensitivity of the criteria in early and late PsA wasdetermined. A total of 106 of the 107 patients with earlyPsA (99.1%; 95% confidence interval [95% CI] 94.9–100)and 176 of 181 patients with late PsA (97.2%; 95% CI93.4–99.1) satisfied the criteria. When patients with earlyPsA were further subdivided on the basis of disease dura-tion, 18 (100%) of 18 with disease duration �6 months,46 (100%) of 46 with disease duration �6 but �12 months,and 42 (98%) of 43 with disease duration �12 months but�2.5 years satisfied the CASPAR criteria. Overall, in the

entire cohort of 288 patients, 282 satisfied the criteria(97.9%; 95% CI 95.5–99.2) at the first clinic visit.

The number of patients satisfying individual items inthe CASPAR criteria set was determined. All patients hadevidence of inflammatory articular disease. In both earlyand late PsA, all patients satisfied the psoriasis criteria,with most having evidence of current psoriasis and the restwith a history of psoriasis. Therefore, a family history ofpsoriasis was not extracted from the database. Ninety-eightpercent were negative for RF. Thus most patients satisfiedthe psoriasis and negative RF criteria. Juxtaarticular newbone formation was seen more often in patients with latePsA (Table 2).

In the entire cohort of 288 patients, 282 satisfied thecriteria. The most common minimal combinations of cri-teria used to meet the CASPAR criteria in these 282 pa-tients were determined. Of the patients who met the cri-teria, 94.7% did so on the basis of having (at least) currentpsoriasis and negative RF; 2.1% on the basis of havingcurrent psoriasis and nail dystrophy; 3.5% on the basis ofa history of psoriasis, negative RF, and nail dystrophy; and3.1% on the basis of history of psoriasis, negative RF, and

Table 1. Demographic and disease characteristics of study patients*

CharacteristicEarly PsA(n � 107)

Late PsA(n � 181)

Total(n � 288)

Male sex, % 67 61 63Age, years 42.1 � 11.9 44.8 � 12.6 43.8 � 12.4Disease duration, years 1.1 � 0.7 11.0 � 8.3 7.3 � 8.2Actively inflamed joint count 9.9 � 8.9 11.3 � 10.4 10.7 � 9.8Swollen joint count 4.1 � 5.2 3.9 � 4.6 4.0 � 4.8Clinically damaged joint count 0.8 � 2.7 5.7 � 10.7 3.8 � 9.0Radiographic damage score† 1.7 � 3.1 6.2 � 9.4 4.6 � 8.0Radiographic damage, % 45 70 61Radiographic sacroiliitis and/or syndesmophytes,

%29 41 37

PASI score 4.6 � 6.1 5.7 � 8.2 5.3 � 7.5

* Values are the mean � SD unless otherwise indicated. PsA � psoriatic arthritis; PASI � Psoriasis Areaand Severity Index.† Modified Steinbrocker method.

Table 2. Number of patients satisfying individual itemson the ClASsification of Psoriatic ARthritis

(CASPAR) criteria*

ItemEarly PsA(n � 107)

Late PsA(n � 181)

Evidence of psoriasis 107 (100) 181 (100)Current psoriasis 102 (95) 167 (92)History of psoriasis 5 (5) 14 (8)

Psoriatic nail dystrophy 82 (77) 133 (74)Negative test for RF 105 (98) 177 (98)Evidence of dactylitis 42 (39) 71 (39)

Current dactylitis 40 (95) 55 (78)History of dactylitis 2 (5) 16 (22)

Juxtaarticular new bone formation 22 (21) 72 (40)

* Values are the number (percentage). PsA � psoriatic arthritis;RF � rheumatoid factor.

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dactylitis. Those who did not meet the criteria had a his-tory of psoriasis and negative RF only.

DiscussionAlthough a number of classification criteria for PsA havebeen used since the 1970s, none have been universallyaccepted (3). Lack of an accepted classification criteria wasa major impediment to epidemiologic, clinical, and ge-netic studies in PsA. Recognizing this, the CASPAR StudyGroup recently developed new classification criteria forPsA (2). The CASPAR criteria were derived from a study ofa large cohort of patients from North America, Europe,Australasia, and Africa, which was to date the largest andmost comprehensive approach by an international groupto develop classification criteria for any rheumatic disease(14). The criteria are simple and highly specific (98.7%),and had a sensitivity of 91.4% in the original study. How-ever, the main limitation of the study was that the patientswith PsA included in the study had longstanding disease(mean disease duration 12.5 years). It was thereforethought that the criteria might not perform well in patientswith early disease (2,14). To address this issue, the presentstudy was undertaken to test the sensitivity of the criteriain early-onset PsA. The results of the study demonstratethat the criteria have a high sensitivity at first clinic visit inboth early and late disease and therefore may be used toclassify patients with recent-onset disease.

The strength of the present study is that all data regard-ing the individual criteria were collected prospectively,according to a standard protocol. This was facilitated bythe fact that the individual items in the criteria set aresimple, well-recognized features of PsA and have beenrecorded prospectively in our database.

A potential drawback of the study was the lack of a goldstandard. This problem plagues evaluation of criteria setsin many rheumatic diseases. Physician diagnosis of thecondition is an accepted surrogate for a gold standard.Indeed, in the CASPAR data set the physician diagnosiswas confirmed both by a committee of 3 individuals exter-nal to the study and by latent class analysis (2). We con-sidered the diagnosis of PsA by an experienced rheuma-tologist who is widely acknowledged to be an expert inPsA as the gold standard.

Most patients satisfied the psoriasis and negative RFcriteria. Because 85% of PsA cases develop either simul-taneously or within 10 years of onset of psoriasis (15), andmost patients are RF negative, it is not surprising thatpatients with early PsA satisfied the CASPAR criteria be-cause most patients at onset have psoriasis and are RFnegative. Additional criteria are required only if patientsdo not have psoriasis. In fact, we demonstrated that �95%of patients who meet the criteria do so on the basis ofhaving current psoriasis and negative RF. Less than 5% ofthe patients were required to have additional criteria,which included history of psoriasis, nail dystrophy, anddactylitis. Moreover, when comparing early and late PsA,only juxtaarticular new bone formation was more preva-lent in late PsA. All other criteria were present in bothgroups in equal proportions.

The CASPAR criteria were developed in patients attend-

ing specialty rheumatology clinics. The present studydemonstrates that the criteria have even higher sensitivityin a subspecialty PsA clinic. Perhaps the most importantissue to be resolved before the CASPAR criteria are ap-plied to more general settings such as primary care orgeneral rheumatology clinics is the definition of inflam-matory arthritis. The CASPAR criteria are to be appliedonly if the patient has inflammatory articular disease,which has not been precisely defined. This did not affectthe present study because patients are required to haveinflammatory arthritis at entry to our clinic. However, ifthe criteria have to be used in more general settings, thebasis for considering the criteria (inflammatory articulardisease: joint, spine, or entheseal) needs to be better de-fined. It would then have to be tested for sensitivity, spec-ificity, predictive value, and accuracy. If the CASPAR cri-teria show high sensitivity and specificity in these settings,they may then be used as both diagnostic and classificationcriteria. Because the criteria are simple and easy to use,this would greatly facilitate population-based epidemio-logic research in PsA.

In conclusion, the CASPAR criteria for the classificationof PsA have a very high sensitivity in both early and latePsA. Most patients satisfy the psoriasis, negative RF, andpsoriatic nail dystrophy criteria.

AUTHOR CONTRIBUTIONS

Dr. Gladman had full access to all of the data in the study andtakes responsibility for the integrity of the data and the accuracyof the data analysis.Study design. Chandran, Schentag, Gladman.Acquisition of data. Chandran, Schentag, Gladman.Analysis and interpretation of data. Chandran, Schentag, Glad-man.Manuscript preparation. Chandran, Schentag, Gladman.Statistical analysis. Schentag, Gladman.

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