Page 124 - Imaging of Osteoarthritis and Rheumatoid Arthritis in Hand Joints
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                                Chapter 7
for synovitis, as long as gadolinium contrast is used. While synovitis can be assessed without contrast by using T2 fat saturated or short tau inversion recovery (STIR) images, it has been shown that reliability is then lower, that low field MRI machines lose sensitivity, and that high field MRI machines become less specific7. Unfortunately low field MRI cannot be advised for detection of bone marrow edema (BME), as the detection rate was poor.
MRI erosions were scored in half of our patients, but it is unlikely that the majority was caused by erosive disease. Half of our patients with early arthritis and inflammatory arthralgia had erosions on MRI, while only 38% of patients developed RA after one year. While some of these erosion-like lesions will be beginning erosions caused by RA, others may be normal anatomy like vascular channels, anatomical variants, or erosion-like pathology caused by other disease or degenerative processes. It is currently unknown what the clinical implications of these MRI erosions are. Recently, in a high-resolution CT study, the definitions of erosions were adjusted to make them more specific for RA 8. Future research should prove if these updates really make the definition more specific for RA, and if so they should also be used for MRI. Until then CT and MRI remain very good for follow-up of bone lesions in RA patients, and by this help in determining disease progression or healing.
Conventional radiography remains the first imaging step to detect erosions in daily practice. CR is widely available, relatively cheap, and has short imaging times for assessment of all hand joints. While ultrasound is less sensitive for detecting erosions than CT and MRI, it is more sensitive for detection of erosions in finger joints than CR. The sensitivity becomes higher if the joint is better accessible with ultrasound, and the joint can be examined from multiple angles. The best sensitivity in the hand is therefore attained in the second and fifth metacarpal head. As specificity of ultrasound-detected erosions is high in comparison with CT and MRI, there is definitely a place for assessment of erosions in MCP and PIP joints while assessing for synovitis as long as the entire joint is scanned.
In the clinical setting, ultrasound remains the first imaging method of choice for detection of synovitis as it is relatively cheap, readily available and has a high specificity for synovitis detection. In the diagnostic process of early

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