Calcium Pyrophosphate Dihydrate Crystal Deposition Disease

(Pseudogout)

A microcrystalline arthritis associated with calcification of hyaline and fibrous cartilage (chondrocalcinosis).

Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease is rare before the 5th decade and becomes more common with age. The mechanism of cartilage calcification is poorly understood but is likely due to many factors. Hyperparathyroidism, acromegaly, and hypothyroidism are predisposing factors.

Symptoms and Signs

The disease was originally called pseudogout to emphasize the acute, episodic, goutlike attacks of synovitis. However, unlike gout, acute CPPD crystal deposition disease usually occurs in large joints, especially the knee, and may involve the shoulder, hip, wrist, and elbow. This disease may cause a chronic, asymmetric, inflammatory polyarthritis, which may mimic rheumatoid arthritis.

Laboratory Findings and Diagnosis

Hematologic findings are nonspecific. Serum calcium levels are normal unless hyperparathyroidism is present. Hyperuricemia may be present and may play a role in pathogenesis. Chondrocalcinosis of the fibrocartilaginous menisci of the knees, the radial and ulnar joints, the symphysis pubis, and the articular disk of the sternoclavicular joint frequently appears on x-ray and supports the diagnosis. In the acute form of this disease, the synovial fluid has a WBC count of 2,000 to 50,000/µL, which is typical of an inflammatory process. Using polarized light microscopy, intracellular and extracellular CPPD crystals can be identified in 90% of effusions. These crystals are generally rhomboid and, unlike urate crystals, are positively birefringent under polarized light.

The diagnosis is based on a clinical history of recurrent, episodic acute attacks and the demonstration of CPPD crystals in synovial fluid. A search for crystals using polarized light microscopy may be necessary, particularly when the patient has polyarticular chronic disease.

Treatment

NSAIDs or a short course of systemic corticosteroids are effective for an acute attack. Intra-articular corticosteroids may be useful when a large joint is involved; colchicine is also effective.