Background/Purpose: High-resolution peripheral quantitative computed tomography (HR-pQCT) is a novel imaging instrument for bony damage in rheumatoid arthritis (RA). Agreement on a case definition for pathologic erosions is required given the sensitivity of HR-pQCT for detecting cortical bone disruptions. The reliability of erosion detection and measurement between readers is crucial to evaluate with this new technology, as HR-pQCT is undergoing validation as an outcome measurement tool.

Methods: HR-pQCT images of the 2^nd and 3^rd metacarpophalangeal joints of RA patients and control subjects were used in an iterative process to achieve consensus on a case definition for erosions. This case definition was applied by 10 independent readers to score 82 joints. Each surface (radial, ulnar, palmar, dorsal) of the proximal phalanx and metacarpal head were characterized for image quality, the presence of a cortical break, the appearance of the cortical defect (physiological or pathological) and a total count of the number of pathologic erosions. Pathologic erosions were further characterized in 2 perpendicular planes for their maximum width and depth.

Results: The case definition of erosion was based on the size and shape of the defect so as to eliminate physiological (eg vessel channel) defects. Of the 656 surfaces analyzed in the reliability exercise, 6 (0.9%) were felt to be of inadequate quality for analysis by the 10 readers and were removed. Inter-reader reliability for erosion detection was excellent with a kappa score of 0.9024 (p<0.0001), with higher kappa scores between experienced readers. Images with discrepant scoring by more than 2 readers were reviewed as a group a second time, with resolution of all cases except for 2 which were lower quality images with multiple bony pathologies overlapping each other(eg vessel channels with superimposed osteophytes masquerading as erosions). Erosion size ranged from 0.16 to 0.89 mm in maximal width and 0.028 to 0.801 mm in maximal depth, with up to 6.3% variability in measurement between readers.

Conclusion: We have devised a new case definition for erosions visualized with a novel sensitive imaging tool. Inter-reader reliability for erosion detection and measurement is high, yielding promise to use HR-pQCT as an outcome measurement tool for bony damage.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/erosion-case-definition-and-scoring-reliability-exercise-using-a-new-outcome-measurement-tool-high-resolution-peripheral-quantitative-computed-tomography-in-rheumatoid-arthritis/