[Diagnosis of crystal-induced arthritis].

Crystal-induced arthritis (CIA) is easy to diagnose as soon as the physician might suspect the diagnosis. Indeed, CIA can be readily ascertained since one single gold standard is available: identification of microcrystals in synovial fluid or in other materials (tophus, synovial tissue biopsy, periarticular tissues). It is therefore mandatory to perform joint aspiration and to get synovial fluid sample for microscopic examination. Monosodium urate crystals are the key feature of gout, and calcium pyrophosphate (CPP) crystals are associated with CPP disease, also called "chondrocalcinosis" in France. Diagnosis of gout can be readily suspected when considering typical clinical presentations such as podagra, presence of tophi, cardiovascular comorbidities, and diuretics use. Plain radiographs, as long as technical quality is present, are an easy way to suspect and eventually to diagnose CPP disease or apatite deposits in any articular or periarticular site. Joint ultrasonography when performed by skilled physicians can easily help in displaying crystal deposits at the cartilage surface (gout) or within the cartilage (CPP), along with peri-tophaceous inflammatory reaction as evidenced by power Doppler.