Background Radiography is considered the gold standard for the detection of bone erosions in Rheumatoid arthritis (RA). Early detection of small erosions may potentially promote timely initiation of treatment and improve outcome. Small cortical breaks cannot be seen on radiographs, but can be detected with High-Resolution peripheral Quantitative Computed Tomography (HR-pQCT). Small cortical breaks can be seen in healthy controls (HCs) and can be the first stages of erosions in RA.
Objectives To compare the number of cortical breaks in hand joints of RA patients and HCs according to their size.
Methods Nineteen subjects (mean age ± SD; 53.9±8.0) from 3 different groups were evaluated: 1) 6 late RA, (diagnosis ≥10 years ago); 2) 6 early RA, (diagnosis ≤2 years ago); and 3) 7 HCs. From these subjects the 2nd MCP and PIP joints were imaged and evaluated with HR-pQCT (isotropic voxel size of 82 μm). In the RA groups, both hands were evaluated (24 joints per RA group), in the HC group only the dominant hand (total of 14 joints). A semi-automated algorithm was applied to the HR-pQCT images for the detection of cortical breaks. First, the outer margin of the bone structure was contoured. Second, the bone within 0.25 mm from this contour was defined as the cortical region. Last, different sizes for defining a cortical beak (>0.50mm, >0.66mm and >0.82mm) were applied and the number of breaks using each cut off was evaluated. Descriptive statistics were calculated and non-parametric tests for comparisons were performed.
Results In the HC group, one joint was excluded due to movement artifacts; therefore, in total 61 joints could be evaluated (Late RA 24 joints, early RA 24 joints, HCs 13 joints). Table 1 shows the total number of breaks of each group stratified per cortical break size. Significant differences were found for break sizes >0.50mm and >0.82mm across the three different groups (p<0.05). These significant differences were found between the HC and late RA group (p<0.05), a trend towards a significant difference was also found between HC and early RA groups with breaks of >0.50mm and >0.66mm (both p=0.07), and between early RA and late RA with breaks of >0.82mm (p=0.06). Most breaks were located close to the rim of the joint (Fig. 1).
Conclusions The number and size of cortical breaks increases over the course of the disease in RA, with a significantly higher number of breaks in late RA compared to HCs. Therefore, the use of HR-pQCT in combination with our semi-automatic algorithm is a promising tool for early detection and monitoring of the number of small cortical breaks.
Disclosure of Interest None declared