MRI, ultrasound offer hope to arthritis patients

Rheumatoid arthritis is characterized by chronic synovial inflammation, resulting in bone erosion and joint destruction. Diagnosis is based on clinical, laboratory, and radiologic findings. Conventional radiography has been the mainstay for diagnosis of joint damage and subsequent follow-up. X-rays can provide only indirect information on synovitis, however, and the modality is insensitive to early bone damage.1 Until recently, the absence of effective treatment to prevent joint destruction limited the need for more sensitive imaging modalities. This situation changed following the introduction of disease-modifying antirheumatic drugs. Availability of these powerful and expensive drugs has created new demands on radiologists to identify patients with aggressive rheumatoid arthritis at an early stage. Treatment decisions can then be taken to prevent joint destruction. MRI and ultrasound can be useful tools in evaluating patients with early rheumatoid arthritis. Both techniques can detect pre-erosive synovial inflammation. They can also identify early bone damage before it becomes apparent on x-rays. MRI can be used to predict future bone damage. It also has a high negative predictive value in patients with clinical suspicion of early rheumatoid arthritis when no evidence of synovial inflammation or bone abnormality is observed. The wrist and the metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints are among the first areas to be affected in rheumatoid arthritis. The most symptomatic extremity, the dominant extremity, or both may be studied with MRI and ultrasound. Abnormalities in early rheumatoid arthritis include synovitis, tenosynovitis, bone erosions, bone marrow edema, and bursitis. Synovitis (rheumatoid pannus) is the earliest pathologic abnormality in rheumatoid arthritis, and it is secondarily responsible for bone and joint damage. It is usually, but not exclusively, bilateral. MRI demonstrates synovitis as synovial enhancement on fat-suppressed gadolinium-enhanced T1-weighted images (Figure 1A), whereas ultrasound detects synovial hyperemia with color or power Doppler imaging (Figure 1B). The degree of hyperemia, and so the importance of the Doppler signal, correlates histologically with the amount of vascularization in the knee.2 Both MRI and ultrasound are more sensitive than clinical assessment in detecting synovitis.3,4 Conventional radiography, on the other hand, is unable to diagnose synovitis unless there is fusiform soft-tissue swelling at the joints. This swelling is often seen at the proximal interphalangeal joints and, to a lesser extent, at the MCP joints. Assessment is subjective and highly dependent on technique. Tenosynovitis is a common finding in patients with early rheumatoid arthritis. Although any tendon may be affected, the flexor digitorum, extensor digitorum, and extensor carpi ulnaris are frequently involved.5 Tenosynovitis is usually, but not exclusively, bilateral. MRI reveals thickening of the synovial sheath with marked enhancement on fat-suppressed Gd-enhanced T1-weighted images. Ultrasound shows similar findings: hypoechoic thickening of the synovial sheath with hyperemia on color or power Doppler imaging (Figure 2). A small amount of fluid may be associated with tenosynovitis. This will show high signal intensity on T2-weighted MRI and low signal intensity on fat-suppressed Gd-enhanced T1-weighted MRI. The fluid appears anechoic on ultrasound, with no evidence of flow on color or power Doppler imaging, and can be expelled from the region by compression with the ultrasound transducer. Affected tendons may appear heterogeneous on both modalities in some patients with early rheumatoid arthritis. This finding is suggestive of incipient tendinitis. The tendinous changes are seen best with ultrasound. Both MRI and ultrasound are more sensitive than clinical assessment in detecting tenosynovitis and outclass conventional radiography, which cannot diagnose the condition at all.