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Operational Definitions and Observer Reliability of the Plain Radiographic Features of Psoriatic Arthritis
WILLIAM J. TAYLOR, GUY G. PORTER, and PHILIP S. HELLIWELL
ABSTRACT.
Methods. Radiographic features were chosen on the basis of a systematic review of the literature. One hundred sixty-four radiographs from 62 patients were selected from various sources by a musculoskeletal radiologist. Radiographs were read independently by 2 observers (WJT, PSH) and scored for the presence or absence of each evaluated feature. Cohen's kappa was used to determine observer agreement beyond chance, and the accuracy of each observer (with reference to the radiologist's judgment) was determined by likelihood ratios. Results. The 2 observers demonstrated similar accuracy, although WJT tended to be more accurate for items classed as absent and PSH more accurate for items classed as present. The following features showed sufficient reliability to be reasonably included in further testing of their discriminatory value (intra- and interobserver kappa values): marginal syndesmophyte (0.68, 0.69), non-marginal syndesmophyte (0.75, 0.59), paravertebral ossification (0.89, 0.79), destructive discovertebral lesion (0.85, 0.65), Romanus lesion (0.64, 0.43), sacroiliitis (0.99, 0.86), entheseal erosion (0.80, 0.71), entheseal ossification (0.69, 0.76), distal interphalangeal erosive disease (0.58, 0.52), joint osteolysis (0.62, 0.47), juxtaarticular bony proliferation (0.43, 0.42), bony ankylosis (0.53, 0.54), tuft osteolysis (0.51, 0.36). The features that showed inadequate reliability were: loss of cortical definition of terminal tuft (0.33, 0.31) and periosteal new bone formation (0.42, 0.03). Conclusion. A number of plain radiographic features of PsA have sufficient reliability to justify inclusion in diagnostic classification criteria sets for further testing. (J Rheumatol 2003;30:2645–58) Key Indexing Terms:
PSORIATIC ARTHRITIS From the Rheumatology and Rehabilitation Research Unit, University of Leeds, Leeds, United Kingdom; and the Department of Radiology, Airedale General Hospital, Keighley, West Yorkshire, United Kingdom. Dr. Taylor was the recipient of the Dorothy Eden Fellowship from the Arthritis Foundation of New Zealand and the Arthritis Research Campaign (Grant No. T0520). W.J. Taylor, MBChB, FRACP, FAFRM, Research Fellow; P.S. Helliwell, MD, PhD, FRCP, Senior Lecturer, Rheumatology and Rehabilitation Research Unit, University of Leeds; G.G. Porter, MD, FRCR, Consultant Radiologist, Department of Radiology, Airedale General Hospital. Address reprint requests to Dr. W.J. Taylor, Rehabilitation Teaching and Research Unit, Department of Medicine, Wellington School of Medicine, University of Otago, PO Box 7343, Wellington, New Zealand. E-mail: wtaylor@wnmeds.ac.nz Submitted April 8, 2002; revision accepted May 13, 2003. |