[Thumb troubles in rheumatoid arthritis].

Thumb involvement may play a relevant role in inducing a severe functional impairment in rheumatoid arthritis. The aim of this sonographic vignette is to show the value of sonography in detailing anatomic changes involving the thumb during a phase of active synovitis. The patient was a 50-year old man who presented with a 3-year history of rheumatoid arthritis. He complained of a 4-week history of a marked recrudescence inflammatory thumb involvement associated with clinical signs of carpal tunnel syndrome. Sonographic images were obtained with a real-time ultrasound system equipped with a 13 MHz linear transducer. Sonographic examination on longitudinal dorsal scan of the metacarpophalangeal joint of the thumb showed a moderate joint cavity widening with two evident bone erosions, one at the metacarpal head and the other one at the basis of the proximal phalanx. The longitudinal volar scan of the first metacarpophalangeal joint confirmed the presence of synovitis detecting a marked joint cavity widening, with aspect of synovial proliferation. The flexor pollicis longus tendon was severely involved (marked tendon sheath widening, synovial proliferation, loss of the normal homogeneous fibrillar echotexture, and a large intratendinous tear). Sonography allowed the depiction of a wide range of otherwise undetectable pathologic changes in the standard clinical setting.