| Discussion: |
Calcium hydroxyapatite crystal deposition disease, a disorder characterized by recurrent painful periarticular calcific deposits (in tendons (calcific tendinitis) and soft tissues or intra-articular calcific deposits.
The shoulder is the site most frequently involved, but the wrist, hand, foot, elbow, hip, neck and lumbar spine may also be affected. Calcium hydroxyapatite crystals are well recognized as a cause of bursitis. Deposition of these crystals appears to play an important role in the degeneration of cartilaginous, osseous and soft tissue structures in and about joints. The deposits usually involve only a SINGLE joint. The existence of familial cases, involvement of many joints, and presence of higher than usual levels of certain histocompatibility antigens may indicate a role for systemic factors in this disease.
Radiographs may reveal a sequence of patterns, with the deposits remaining static in some patients for long periods of time and enlarging or even disappearing in others.
Intra-articular calcium hydroxyapatite crystal deposition is also known to occur and may be responsible for an arthropathy termed the Milwaukee shoulder syndrome, in which intra-articular deposition of calcium hydroxyapatite crystals is followed by release of enzymes. The enzymes attack the periarticular tissues, including the rotator cuff, and rotator cuff disruption ensues.
Crystals may become deposited in the synovial membrane, in the joint capsule, or occasionally in cartilage (chondrocalcinosis). Structural joint damage (Milwaukee shoulder, cuff tear arthropathy) may also be observed. An association of arthropathy in the shoulder and arthropathy in other joints, especially the knee, hip and small joints of the hand and feet, has been reported.
Radiographically, the appearance of deposits is similar to that of calcium pyrophosphate dihydrate crystal deposition disease. Generally the calcifications appear as homogeneous, cloudlike intra-articular radiodense shadows.
In some patients synovial fluid or cartilage may reveal both calcium hydroxyapatite and calcium pyrophosphate dihydrate crystals, a condition termed mixed calcium phosphate crystal deposition disease. This disorder should be suspected if radiographs reveal both extensive cartilage calcification and diffuse intra-articular and capsular calcification or dense, homogeneous calcific collections of tendons.