RADIOLOGICAL ASSESSMENT IN PSORIATIC ARTHRITIS

Transcription

1 British Journal of Rheumatology 1998;37: RADIOLOGICAL ASSESSMENT IN PSORIATIC ARTHRITIS P. RAHMAN, D. D. GLADMAN,* R. J. COOK, Y. ZHOU, G. YOUNG and D. SALONEN Department of Medicine and Institute of Medical Sciences, University of Toronto, *Department of Medicine, University of Toronto and Psoriatic Arthritis Program, The Toronto Hospital Rheumatic Disease Unit, Department of Statistical and Actuarial Science, University of Waterloo, Waterloo, Ontario, University of Waterloo, Waterloo, Ontario, Psoriatic Arthritis Clinic, University of Toronto and Department of Medical Imaging, University of Toronto, Toronto, Canada SUMMARY Our objective was to compare the reliability and responsiveness of the original Steinbrocker s (OS), our modified Steinbrocker s (MS) and Larsen s (L) radiological scoring methods for detecting radiological change in psoriatic arthritis over time. Two sets of radiographs of the hands and feet at least 2 yr apart were selected from 68 patients. Films were randomly presented and scored independently by a rheumatologist (DDG) and a radiologist (DS), in a blinded fashion using all methods. The index of reliability was the intraclass coefficient (ICC) and the responsiveness was assessed using plots and regression analyses. All three radiological scoring methods have excellent interobserver and good intra-observer reliability. L and MS are equally responsive and superior to OS in detecting change in joint damage over time. Thus, the L or MS radiological scoring methods can be used to monitor disease progression in psoriatic arthritis. KEY WORDS: Psoriatic arthritis, Radiological methods, Larsen s method, Steinbrocker s method, Validity, Responsiveness. THE plain radiograph of the joints is considered the psoriatic arthritis longitudinally and monitor disease current standard for assessing disease progression in progression should be valid, easy to administer, rapid inflammatory arthritis. In particular, radiographs of and economically feasible. Larsen s and Steinbrocker s the hands and feet have been most widely used for this methods fulfil these requirements if adequately valid- purpose. The first standardized radiological scoring ated, as suggested by the methodological framework method was devised by Steinbrocker et al. in 1949 [1]. by Bombardier and Tugwell [15] (content validity, face Since then, numerous scoring methods have been pro- validity, criterion validity, discriminant validity and posed which differ greatly in the type of abnormalities construct validity). they are designed to capture and the number of joints The objective of our study was to compare the that are scored [2 9]. All the scoring methods evaluating reliability, reproducibility and responsiveness of peripheral joints were developed for patients with the original Steinbrocker s method, our modified rheumatoid arthritis. At present, there is no single Steinbrocker s method and Larsen s method for method that has achieved universal acceptance. The detecting radiological change in psoriatic arthritis scoring methods by Larsen et al. [10], Steinbrocker over time. et al. [1] and Sharp et al. [11] appear to be the most commonly reported for evaluating radiographic METHODS changes and quantifying damage. While these methods Patients have been validated in rheumatoid arthritis [12, 13], The radiographs were selected from the University similar studies in psoriatic arthritis are lacking. of Toronto Psoriatic Arthritis Clinic. This clinic was Radiographic changes in psoriatic arthritis differ from established in 1978 and since then has been enrolling those in rheumatoid arthritis, as evidenced by lower patients with psoriatic arthritis as part of an ongoing frequency of periarticular osteopenia, higher preval- prospective study. Patients were assessed every 6 12 ence of distal interphalangeal erosions, along with the months, at which time a standardized history, physical presence of tuft changes, pencil-in-cup changes, bony examination and laboratory evaluation were completed proliferation, periostitis and bony ankylosis in psoriatic and entered into a computerized database. Routine arthritis. Since most scoring methods involve assess- radiographs of the hands, feet, spine and sacroiliac ment of erosions and joint destruction, it seems prudent joints were completed at 1 2 yr intervals. to validate specifically radiological methods in psoriatic arthritis. Scoring methods already validated in rheum- Radiographic assessment atoid arthritis were chosen as both conditions are From our cohort, radiographs of 68 patients with a inflammatory arthropathies and share histological fea- wide spectrum of disease were selected by an independtures which eventually lead to joint destruction [14]. ent physician who was not involved in interpreting the The ideal radiological scoring method to follow films. Two sets of posteroanterior radiographs of the hands and feet at least 2 yr apart were obtained for each patient. Prior to reading the films, a training Submitted 18 July 1997; revised version accepted 27 February session was held to review the scoring methods. For Correspondence to: D. Gladman, Main Pavilion, The the Steinbrocker method, each of the distal inter- Toronto Hospital, Western Division, 399 Bathurst Street, Toronto, phalangeal, proximal interphalangeal and metacarpo- Ontario M5T 2S8, Canada. phalangeal joints of the hand, the wrist, and the British Society for Rheumatology

2 RAHMAN ET AL.: RADIOLOGICAL ASSESSMENT IN PSORIATIC ARTHRITIS 761 metatarsophalangeal and first interphalangeal joint of tiple assessment on each patient. Analysis was carried the feet were scored. The wrist was counted as a single out based on overall mean scores and location-specific joint. Each joint was judged on a 0 4 scale (Table I). mean scores. For assessing both the interobserver and For the original Steinbrocker s method, a single score intra-observer reliability, analysis of variance was conwas assigned according to the status of the worst joint ducted with a random patient effect. Let s2 and s2 s r [1]. We felt that the assignment of a single global score denote the variance components reflecting subject to would make this method insensitive to detect changes, subject and observer variability. The index of reliability thus Steinbrocker s method was modified to record the adopted is the interclass correlation coefficient ( ICC) score of each individual joint assessed, using the scale given by ICC = s2/(s2 + s2) [18]. Our objective in s s r in Table I. Thus, our modified Steinbrocker method is fitting these models was to obtain estimates for the based on the same scale, but provides a more detailed ICC for Larsen s and both Steinbrocker s methods, method of scoring. For Larsen s method, the joints and to compare them. scored were of a similar distribution and each joint Regarding the responsiveness analysis, as there was was graded according to a 0 5 scale in accordance no gold standard for measuring joint damage, we were with Larsen s method as modified by Rau and Hehborn restricted to making comparisons of change scores [16] (Table I). The distal interphalangeal joint, as well between instruments. The extent to which change sugas the first metatarsophalangeal and interphalangeal gested by one instrument related to change by another joint of the feet, were added to the original Larsen s was used. The responsiveness was measured by plotting method as these joints are frequently affected in psori- the change scores between baseline and 2 yr for both atic arthritis. The index was expressed as a mean of methods, along with regression analysis. The indices all individual areas rather than an aggregate score, as of interest include the r2, and the slope of the best suggested by Larsen for evaluating radiographs for fitting regression line. A slope near one would indicate long-term studies [ 17]. that two methods being compared are reacting to The films were presented to the observers in a changes to approximately the same degree. Of course random order and were scored in a blinded fashion. the scoring methods given in Table I must be borne in The radiographs were read independently by an experienced mind when interpreting these results. rheumatologist (DDG) and a radiologist (DS) with an expertise in musculoskeletal radiography using RESULTS all methods. Twenty radiographs were recirculated to The demographics of the 68 patients are listed in the observers and were again presented in a random Table II. The Larsen and both Steinbrocker methods order to determine the intra-observer variability. Any all showed excellent interobserver reliability as measured joint demonstrating radiographic alterations exclusively by the ICC. The interobserver ICC for Larsen s due to degenerative arthritis was excluded, as the method was 0.87 (95% CI: 0.79, 0.92); for the original purpose of the study was to evaluate methods to detect Steinbrocker s method it was 0.86 (95% CI: 0.76, 0.90) alterations in psoriatic arthritis. and for the modified Steinbrocker s method it was 0.86 (95% CI: 0.76, 0.90). All methods also showed Analysis good intra-observer reliability for each observer. For In order to assess the interobserver reliability, only Larsen s method, the intra-observer ICC was 0.84 baseline measurements were used to ensure that (95% CI: 0.62, 0.94) for DS and 0.85 (95% CI: 0.64, the assumption of independence across patients was 0.95) for DDG. For the original Steinbrocker s achieved. To assess reliability based on standard statistical method, the intra-observer ICC was 0.90 (95% CI: methods, assumptions of approximate normality 0.74, 0.96) for DS and 0.86 (95% CI: 0.65, 0.95) for of scores are made. Individual joint assessments are DDG. Finally, for the modified Steinbrocker s, the very discrete and highly skewed, so overall mean intra-observer ICC was 0.80 (95% CI: 0.52, 0.92) for ratings and mean ratings by joint location were examined. DS and 0.81 (95% CI: 0.59, 0.93) for DDG. As all Intra-observer reliability was measured with mul- ICC values were >0.5, the variance of error term was always smaller than the variance of the patient effect. TABLE I Grading for Steinbrocker s and modified Larsen s method In terms of comparing Larsen s method with the two Steinbrocker s methods, since the confidence intervals overlap with each other, there is no statistically Steinbrocker s method 0 Normal 1 Soft-tissue swelling/osteopenia TABLE II 2 Erosion Demographics of study population (68 patients) 3 Erosion plus joint space narrowing 4 Total joint destruction Mean S.D. Modified Larsen s method 0 Normal Age at presentation to clinic (yr) Soft-tissue swelling, osteoporosis, slight joint space narrowing Arthritis duration Erosion with destruction of joint surface (DJS) <25% Age at onset of arthritis Erosion with DJS 26 50% Number of active joints Erosion with DJS 51 75% Number of effusions Joint destruction, DJS >75% Number of damaged joints

3 762 BRITISH JOURNAL OF RHEUMATOLOGY VOL. 37 NO. 7 significant difference among the methods with respect In our study, Larsen s and both the original and to interobserver or intra-observer reliability. modified Steinbrocker s methods all showed excellent In order to assess whether these radiographic scoring interobserver reliability with an ICC of 0.87, 0.86 and methods were able to detect change in psoriatic arthand 0.86, respectively. These correlations are quite high ritis, the change scores of the instruments were comoid similar to those reported in studies with rheumat- pared with each other. The relative responsiveness of arthritis [8]. The consistency among each reader Larsen s vs Steinbrocker s method as measured by the was also high as the intra-observer reliability for slope of the regression line was 0.15 (95% CI: 0.06, Larsen s was 0.84 and 0.85 for DS and DDG, respect- 0.24) for DS and 0.09 (95% CI: 0.001, 0.19) for DDG ively; for the original Steinbrocker s, it was 0.90 and (Fig. 1a and b, respectively). Thus, the original 0.86 for DS and DDG, respectively, and for the Steinbrocker s was not as sensitive in detecting radioand modified Steinbrocker s it was 0.80 and 0.81 for DS graphic change as Larsen s for both examiners. In DDG, respectively. The combination of excellent contrast, the slope of Larsen s vs the modified agreement between the two observers and the high Steinbrocker s method was 1.1 (95% CI: 1.0, 1.1) for consistency of each observer suggests that all methods DS and 0.93 (95% CI: 0.80, 1.0) for DDG (Fig. 2a are reliable. and b, respectively). Thus, Larsen s and the modified A radiographic scoring method should not only be Steinbrocker s were of comparable responsiveness for reliable, but also sensitive to change. As suspected, change for both examiners. the original Steinbrocker s was relatively insensitive to detect changes over time as this expedient method omitted a significant amount of information. DISCUSSION Meanwhile, the Larsen and the modified Steinbrocker Steinbrocker s is a simple scoring method, initially methods were equally responsive to change by both devised in 1949, which is still widely used today. It examiners. Thus, these two radiographic methods can assesses global changes and gives an overall measure be used to detect change in psoriatic arthritis. of joint damage from 0 to 4. The severity of radiological In applying the concepts of the validity criteria involvement is scored by assessing the degree of soft- [15], as they relate to the assessment of a radiotissue swelling, osteopenia, joint space narrowing, mal- graphic scoring method, the Larsen s and modified alignment and bony ankylosis. It is performed rapidly Steinbrocker s methods both appear to be valid. and thus is quite useful in clinical practice. No radio- Content validity (choice and the relative importance graphic standards are employed in using this method. given to each component appropriate for the method) Larsen s method was introduced in 1977, and has and face validity (method of aggregating the individual been modified on numerous occasions [16, 19, 20]. components into a score) appear to be justified as the Similar to Steinbrocker s method, Larsen s assesses the components (soft-tissue swelling, osteoporosis, erojoint globally. Scores range from 0 to 5 depending on sions, joint space narrowing, and destruction) reflect the extent of osteoporosis, joint space narrowing, ero- an orderly sequence of the pathogenic, histological and sions and joint destruction. This method is based on radiological stage resulting in joint damage. Criterion standard radiographs in an attempt to improve repro- validity (the method produces consistent results that ducibility. Rau modified Larsen s method by quantify- reflect the true clinical state of the patient) is confirmed ing the extent of joint space destruction required to for both methods by our results as the ICC for attain stages 2 5 [16]. Larsen s method theoretically interobserver reliability and intra-observer reliability may be more responsive for detecting change than was quite high, suggesting excellent consistency of the Steinbrocker s for any given joint as this index has an methods. With respect to discriminant validity (detects additional stage to detect change. smallest clinically significant differences), Larsen s and Sharp s method was developed in 1971 [21] and modified Steinbrocker s methods both detect change modified in 1985 [11]. Erosions and joint space nar- over time and were equally responsive. It is not possible rowing are scored separately in this method for a total to ascertain whether the radiological change detected of 35 observations in each hand. This detailed analysis was the smallest clinically significant difference as there provides a greater sensitivity and amplitude to change is no clinical outcome measure which represents the than Larsen s and Steinbrocker s methods in patients minimal radiological change considered clinically signiwith rheumatoid arthritis [ 13]. However, Sharp s ficant for comparison. Construct validity (the method method may not be as sensitive in detecting changes agrees with expected results based on the hypothesis in psoriatic arthritis as compared to rheumatoid arth- of the investigator) seems justified as Larsen s and ritis, since the erosions and new bone formation in Steinbrocker s methods detect change which mimics psoriatic arthritis are often para-marginal or involve pathophysiological changes and these methods have the shaft of the phalanges. These lesions would not be been previously validated in rheumatoid arthritis, accounted for by Sharp s method, as it detects discrete which is an inflammatory arthritis with many features intra-articular erosions and joint space narrowing, similar to psoriatic arthritis. Finally, Larsen s and unlike Larsen s and Steinbrocker s methods that score Steinbrocker s methods are feasible in a clinical practhe joint globally. Sharp s method was not assessed in tice as they are easy to score, not time consuming and our study as it is quite time consuming to perform and relatively inexpensive. felt not to be very practical in a clinic setting. Thus, from our study we conclude that Larsen s and

4 RAHMAN ET AL.: RADIOLOGICAL ASSESSMENT IN PSORIATIC ARTHRITIS 763 FIG. 1. (a) Responsiveness analysis of Larsen vs original Steinbrocker (DS). (b) Responsiveness analysis of Larsen vs original Steinbrocker (DDG).

5 764 BRITISH JOURNAL OF RHEUMATOLOGY VOL. 37 NO. 7 FIG. 2. (a) Responsiveness analysis of Larsen vs modified Steinbrocker (DS). (b) Responsiveness analysis of Larsen vs modified Steinbrocker (DDG).

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7 766 BRITISH JOURNAL OF RHEUMATOLOGY VOL. 37 NO. 7 BRHEUM MSS No. 7A/1032 Radiological assessment in psoriatic arthritis P. Rahman, D. D. Gladman, R. J. Cook, Y. Zhou, G. Young and D. Salonen 000