Detection of bone erosions in early rheumatoid arthritis: 3D ultrasonography versus computed tomography

Three-dimensional (3D) volumetric ultrasonography (US) is an interesting tool that could improve the traditional approach to musculoskeletal US in rheumatology, due to its virtual operator independence and reduced examination time. The aim of this study was to investigate the performance of 3DUS in the detection of bone erosions in hand and wrist joints of early rheumatoid arthritis (ERA) patients, with computed tomography (CT) as the reference method. Twenty ERA patients without erosions on standard radiography of hands and wrists underwent 3DUS and CT evaluation of eleven joints: radiocarpal, intercarpal, ulnocarpal, second to fifth metacarpo-phalangeal (MCP), and second to fifth proximal interphalangeal (PIP) joints of dominant hand. Eleven (55.0 %) patients were erosive with CT and ten of them were erosive also at 3DUS evaluation. In five patients, 3DUS identified cortical breaks that were not erosions at CT evaluation. Considering CT as the gold standard to identify erosive patients, the 3DUS sensitivity, specificity, PPV, and NPV were 0.9, 0.55, 0.71, and 0.83, respectively. A total of 32 erosions were detected with CT, 15 of them were also observed at the same sites with 3DUS, whereas 17 were not seen on 3DUS evaluation. The majority of these 3DUS false-negative erosions were in the wrist joints. Furthermore, 18 erosions recorded by 3DUS were false positive. The majority of these 3DUS false-positive erosions were located at PIP joints. This study underlines the limits of 3DUS in detecting individual bone erosion, mostly at the wrist, despite the good sensitivity in identifying erosive patients.