Further observations on the arthropathy of calcium pyrophosphate crystal deposition disease.

The arthropathy of calcium pyrophosphate dihydrate (CPPD) crystal deposition disease is distinctive and may affect lumbar spinal and sacroiliac joints, as well as appendicular joints. Subchondral pseudocysts that are a hallmark of the disease have a variable appearance, but often occur as a typical cluster of subchondral, coalescent lucencies with smudged, sclerotic margins. Structural joint collapse with fragmentation of cartilage and bone may occur and appear to be related, at least in some cases, to antecedent pseudocysts. Characteristic intra-articular osteochondral bodies are often extensive and may affect multiple joints; their pathogenesis is discussed. Articular synovial calcification is common and may be due to calcium hydroxyapatite, as well as CPPD, particularly if advanced degenerative changes are present. Recognition of the radiologic features may be encountered in CPPD crystal deposition disease is important for differential diagnosis.