[Imaging techniques in rheumatology: sonography in rheumatoid arthritis]

Musculoskeletal ultrasonography has become an important diagnostic tool in rheumatoid arthritis. In Germany it is part of the rheumatology training, and many ultrasound courses provide further education. Only in the last five years the international importance of ultrasound in rheumatology has increased dramatically. Sonography can be performed as a bedside procedure and as an extension of the clinical investigation. It is easily tolerated by the patients, and it can be repeated any time. Sonography can have a great impact on therapeutic decisions. A > or = 5 MHz linear transducer is needed. Most transducers that are used for musculoskeletal ultrasound have about 7.5 MHz. Modern transducers with higher frequencies (>7.5 MHz) and high resolution improve the diagnostic value of the investigation. Sonography is superior to plain radiography to detect erosions as far as the region is accessible by ultrasound. It is more sensitive than the clinical investigation for the detection of synovitis, tenosynovitis, tendinitis, and bursitis as well as for the differentiation of these lesions. Color Doppler sonography aids in evaluating the activity of inflammation and in differentiating intraarticular structures. Carpal- and ulnar neuropathy occur secondary to rheumatoid arthritis and may lead to characteristic nerve swelling. Ultrasound-guided injections into joints and tendon sheets can be performed.