Background Diagnosis and monitoring of patients with rheumatoid arthritis (RA) is largely based on radiographs, therefore the sensitivity to detect small changes of bone erosions is limited. This is also true for MRI, where the spatial resolution is limited.
Objectives To use high resolution peripheral quantitative CT (HR-pQCT) combined with advanced 3D image processing to quantify longitudinal shape and size changes of bones erosion of the metacarpophalangeal (MCP) joints of patients with RA.
Methods HR-pQCT images of the second to fourth MCP joint from 10 RA patients were acquired on an XtremeCT scanner (Scanco Switzerland) with an isotropic voxel size of 82µm. Patients were scanned at baseline and after 1.1±0.4 years. 5 patients were treated with Methotrexate (MTX, mean age±SD 53.1±18.8 years, 1 male), 5 with tumor necrosis factor inhibitors (TNFi, 46±13.9 years, all women). The periosteal surface was segmented independently in baseline (BL) and follow-up (FU) datasets. The BL segmentation was rigidly registered to the FU segmentation and also used for the FU images. Erosions were segmented independently in both BL and FU data. We evaluated change in volume, surface area, and sphericity (a measure between 0 and 1 for how closely the erosion resembles a sphere). We also dilated the erosions to obtain 4 concentric volumes of interests (VOIs) in which BMD was measured.
Results 10 erosions in the MTX group and 11 erosions in the TNFi group were evaluated. Mean±SD (min/max) % changes of volume, surface area and sphericity were 0.58±18.78 (-20.91/26.28), 4.7±19.9 (-23.93/35.45) and -3.01±10.36 (-24.73/12.44) in the MTX group and -13.97±37.92 (-63.68/75.1), -10.7±33.03 (-60.97/38.23) and 4.73±21.6 (-19.28/61.04) in the TNFi group. % BMD changes in the dilated VOIs 1 to 4 were 0.6±13.64, 2.16±15.2, -0.22±11.07 and -2.55±6.06 for the MTX group and 10.83±21.62, 15.84±27.01, 12.4±19.05 and 9.14±13.56 for the TNFi group. The % change in erosion volume negatively correlated with the % change in BMD in VOI 1 to 4. For all 21 erosions combined, Spearman’s rho were -0.49, -0.54, -0.54 and -0.5. All correlations were significant (p<0.05). Intra-operator BMD precision (root mean squares coefficients of variation) ranged from 2.66% (VOI1) to 3.73% (VOI3).
Conclusions In this small pilot study we demonstrated that shape and volume changes of bone erosions of the MCPs can be quantified and that small BMD changes in the vicinity of the erosions can be detected. Our preliminarily analysis indicated differences in erosion volume and surrounding BMD changes between the two groups, however, the initial results were not adjusted for age and other potential covariates. A limitation of the HR-pQCT technique is a loss of precision due to motion artifacts, due to long scan times (∼8min).
Disclosure of Interest None Declared
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