Musculoskeletal ImagingCalcium pyrophosphate dihydrate crystal deposition disease
a disorder marked by deposition of calcium pyrophosphate dihydrate (CPPD) crystals within
cartilage (termed
chondrocalcinosis), which leads to a distinctive goutlike pattern of arthritis (
pseudogout syndrome) and structural joint damage (
pyrophosphate arthropathy). Various clinical patterns of CPPD crystal deposition disease may occur. In addition, numerous pathologic conditions are associated with deposition of CPPD crystals (Table 1).
Calcium pyrophosphate dihydrate crystal deposition disease, Table 1. Some conditions associated with CPPD crystal deposition.
The CPPD deposits may occur in cartilage (both hyaline and fibrocartilaginous), synovium, capsule, tendons, and ligaments. Chondrocalcinosis is most frequent in the knees, wrists, symphysis pubis, elbows and hips. Deposits in fibrocartilage appear on radiographs as thick, shaggy, irregular radiodense areas with a predilection for the central aspect of the joint cavity. Hyaline cartilage calcifications are thin and linear on radiographs; they may be seen parallel to and separated from the subjacent subchondral bone. In general, chondrocalcinosis of more than one set of joints usually indicates CPPD crystal deposition disease (as opposed to calcium hydroxyapatite crystal deposition disease).
The structural joint damage (pyrophosphate arthropathy) resembles the changes in degenerative joint disease both pathologically and radiographically; however, the pattern and distribution show distinctive features. Pyrophosphate arthropathy is most common in the knee, wrist and metacarpophalangeal joints. Usually the joints are involved bilaterally. Cartilage fibrillation, erosion partial or complete denudation, and joint space narrowing are typical findings. Thickened trabeculae and multiple cysts are found in subchondral bone. The cysts of CPPD crystal deposition disease typically are larger, more numerous, and of more widespread distribution than those in degenerative joint disease. Bone fragmentation and collapse are frequent, but bone erosion is not a typical feature, and intra-articular osseous bodies may exist loose within the joint cavity or embedded in the cartilaginous and synovial tissue. Pyrophosphate arthropathy differs from degenerative joint disease in the following five ways:
· unusual articular distribution;
· unusual intra-articular distribution;
· prominent subchondral cyst formation; and
· presence of severe and destructive progressive bone changes at times resembling those of neuropathic osteoarthropathy; and
· variable osteophyte formation
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