Musculoskeletal ultrasound may be useful to discriminate between similar arthritic entities. In case of suspected crystalline arthropathy, sonography may identify calcium pyrophosphate deposition (CPPD) or monosodium urate (MSU) crystals with a high sensitivity and specificity. At large joints CPPD crystals typically appear as thin hyperechoic bands and/or hyperechoic sparkling spots within hyaline cartilage whereas MSU depositions are observed as hyperechoic enhancements (homogeneous thickening or focal deposition) of the superficial margin of articular cartilage causing the “double contour” sign. At wrists or knees, CPPD deposits may also appear as hyperechoic rounded areas within the fibrocartilage. In small joints, CPPD crystals may imitate a double contour sign; however, at dynamic investigation deposits are displaceable whereas MSU crystals “stick” at the hyaline cartilage. An intratendinous tophus usually causes disarrangement of fibrillar echotexture and cloudy hyperechogenic bands which may generate an acoustic shadow. CPPD calcifications of tendons are typically linear and may be extensive. In summary, characteristic ultrasound findings at joints, fibrocartilage and tendons may help to distinguish between gout and pseudogout in patients with suspected crystalline arthropathy.
Disclosure of Interest None Declared