Background The coexistence of both urate and calcium pyrophosphate (CPP) crystals in the same synovial fluid has been reported by many authors. The evaluation of crystal deposits in mixed microcrystallic arthropathy by imaging is essential for the diagnosis and management of both diseases. It is especially important for the diagnosis of calcium pyrophosphate deposition disease (CPPD) that is paid a little attention.

Objectives To evaluate to usefulness of plain radiography (Rg), computed tomography (CT) and Doppler ultrasonography (US) in presenting specific images of monosodium urate (MSU) and CPP deposits in patients with gout and CPP crystals in synovial fluid.

Methods 15 pts (14m/1f), mean age 59 years, mean disease duration 12 years, with crystal-proven gout and the presence of CPP crystals in synovial fluid (SF) were enrolled. All patients had arthritis and underwent aspiration of SF from inflamed joint (11 knees, 4 I MTPs). 6 patients had acute, 9 – chronic arthritis. Mean number of joints involved – 4, intradermal tophi were recorded in 10 patients (elbows, helix). Crystal identification was performed using polarised light microscopy with compensator (Olympus). Rg, CT and US of the knee joints were made in all patients. CT was obtained using a lightspeed VCT Select (GE), US – with Volusion-I (GE). Rg and CT evidence of cartilage calcification (CC) included thick linear linear deposits in hyaline cartilage, parallel to and separated from subchondral bone. Rg feature of tophi was erosion with sclerotic rim. CT identification of tophi included round and oval opacities with density about 170 HU. US CPP crystal deposition features were taken as linear hyperechoic deposits in the hyaline cartilage. US feature of urate deposition double-contour sign included hyperechoic bright contour following the contour of the bone surface – double contour sign.

Results Rg and CT evidence of cartilage CC were disclosed in 60% and 87% of pts, correspondingly. Rg showed intraosseus tophi in 27% of pts. CT revealed intraosseous tophi in 47%, tophi in soft tissues around the knees– in 27% of pts. US appeared to provide CC features and double-contour sign in 100% of pts and revealed tophi in soft tissues around the knees in 30% of pts.

Conclusions US demonstrated features of both diseases - chondrocalcinosis and double-contour sign – in all patients with MSU and CPP crystals in SF. Besides, US enabled us to see tophi in soft tissues in 30% of pts. CT discloses intraosseous tophi two times more often than Rg. Usefulness of CT in the revealing of CC is 2 times higher than Rg, mostly because of detailed visualization of patello-femoral CC. Moreover, CT, not Rg, has the possibility of revealing tophi in soft tissue that is almost identical to US.

Disclosure of Interest None Declared