Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


Application of High-Resolution Peripheral Quantitative Computed Tomography (HR-pQCT) To Quantify Bony Damage in Rheumatoid Arthritis.

Barnabe1,  Cheryl C. M., Martin1,  Liam, Boyd2,  Steven K., Barr1,  Susan G.

University of Calgary, Calgary, AB, Canada
University of Calgary

Background:

High-resolution peripheral quantitative computed tomography (HR-pQCT) (isotropic voxel size of 82 mm) provides three-dimensional information on bone microarchitecture. We investigated the ability of HR-pQCT to provide quantitative assessments of features of RA bony damage, and diagnostic performance.

Methods:

Fifteen patients with established RA and damage of the MCP or PIP joints and 15 age- and sex-matched control patients were recruited and scanned by HR-pQCT (XtremeCT; Scanco Medical, Switzerland). A semi-automated segmentation method identified bone mineral based on changes in the gray-scale, with manual correction of any errors made by the program. These images were used to create a three-dimensional reconstruction of the joint. The minimum joint space width was calculated by counting the number of voxels between articular surfaces (Image Processing Language). The number and location of erosions were assessed visually from the two-dimensional images. Quantitative measures of bone density were obtained for the 2nd, 3rd and 4th MCP joints. Diagnostic test performance for HR-pQCT compared to the clinical diagnosis of RA was calculated. Reproducibility was assessed by re-contouring a subset of the images.

Results:

Joint space narrowing was detected in RA patients compared to controls (Table 1). In RA, the majority of erosions occurred at the proximal bone surface (mean 23.6 (SD 17.6)). Some controls were found to have erosions, mainly in the IP and PIP joints. Quantitative assessment of bone density parameters did not reveal significant differences between RA patients and controls (Table 2). The best test performance for the clinical diagnosis of RA was determination of an erosion in MCP2 (sensitivity 76.9%, specificity 93.3%, ROC area 0.851, positive likelihood ratio 11.5 (95%CI 1.7–78.4)). Reproducibility was good for bone density parameters (all root square mean coefficients of variance were under 1%), but less so for joint space measurements (17%), perhaps related to difficulties in contouring angulated joints.

Table 1. Relative (and standard deviation) joint space of controls compared to RA patients (positive value indicates the control has a wider joint space).

 PIP 2PIP 3PIP 4PIP 5MCP 2MCP 3MCP 4MCP 5
Difference (mm)71 (171)167 (247)-68 (181)44 (196)131 (535)262 (502)106 (406)145 (287)

Table 2. Relative (and standard deviation) bone density parameters of controls compared to RA patients (positive value indicates that the parameters is higher in controls).

ParameterMCP 2MCP 3MCP 4
Whole bone density (mg/cm3).07 (66)-8.91 (46)-24.6 (96)
Cortical density (mg/cm3)21.05 (60)14.21 (53)-19.55 (90)
Trabecular density (mg/cm3)6.13 (48.6)-1.19 (33.8)-18.34 (67.3)
Average cortical thickness (mm).007 (.047)-.004 (.037)-.015 (.046)
Average trabecular number (mm-1)-.04 (.20)-.01 (.21)-.36 (1.16)
Average trabecular thickness (mm)-.004 (.03)-.002 (.03)-.010 (.02)
Average trabecular spacing (mm).003 (.07)-.014 (.06).006 (.06)

Conclusions:

We have developed methods to provide quantitative measurements of bony damage in established RA using HR-pQCT. Differences in joint space width are most pronounced at the MCP joints. Erosions at MCP2 are highly specific for RA, but erosions were detected in controls unrelated to clinical disease. A larger sample size may reveal detectable differences in bone density parameters between subjects with active inflammatory arthritis and those without. In this preliminary study, HR-pQCT demonstrated good performance characteristics for RA diagnosis.

To cite this abstract, please use the following information:
Barnabe, Cheryl C. M., Martin, Liam, Boyd, Steven K., Barr, Susan G.; Application of High-Resolution Peripheral Quantitative Computed Tomography (HR-pQCT) To Quantify Bony Damage in Rheumatoid Arthritis. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :119
DOI: 10.1002/art.27888

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