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Calcium Pyrophosphate Dihydrate Crystal Deposition Disease
Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease involves intra-articular and/or extra-articular deposition of CPPD crystals. Manifestations are protean and may be minimal or include intermittent attacks of acute arthritis, termed pseudogout or acute Ca pyrophosphate crystal disease, and a degenerative arthropathy that is often severe. Diagnosis requires identification of CPPD crystals in synovial fluid. Treatment of pseudogout attacks is with intra-articular corticosteroids or oral glucocorticoids, NSAIDs, or colchicine.
CPPD crystal deposition (chondrocalcinosis), whether symptomatic and asymptomatic, becomes more common with age.
Asymptomatic chondrocalcinosis is common in the knee, metacarpophalangeal joints, wrist, symphysis pubis, and spine. Men and women are affected about equally.
The cause of CPPD crystal deposition disease is unknown. Frequent association with other conditions, such as trauma (including surgery), hypomagnesemia, hyperparathyroidism, gout, hemochromatosis, and old age, suggests that CPPD crystal deposits are secondary to degenerative or metabolic changes in the affected tissues.
Some cases are familial, usually transmitted in an autosomal dominant pattern, with complete penetration by age 40.
Recent studies indicate that the ANK protein is a central factor in producing excess extracellular pyrophosphate, which promotes CPPD crystal formation. ANK protein is a putative transporter of intracellular pyrophosphate to the extracellular location where CPPD crystals form.
Acute, subacute, or chronic arthritis can occur, usually in the knee or other large peripheral joints; thus, Ca pyrophosphate crystal disease can mimic many other forms of arthritis. Acute attacks are sometimes similar to gout but are usually less severe. There may be no symptoms of CPPD crystal deposition disease between attacks or continuous low-grade symptoms in multiple joints, similar to RA or osteoarthritis. These patterns tend to persist for life.
CPPD crystal deposition disease should be suspected in older patients with arthritis, particularly inflammatory arthritis.
Diagnosis of CPPD crystal deposition disease is established by identifying rhomboid- or rod-shaped crystals in synovial fluid that are not birefringent or are weakly positively birefringent on polarized light microscopy. Joint fluid in acute attacks has findings typical of inflammation; thus, coincident infectious arthritis and gout (other common causes of inflammatory joint fluid), must also be excluded. Infectious arthritis is ruled out based on Gram stain and culture findings. Gout is usually best ruled out by the absence of urate crystals in fluid from the inflamed joint. X-rays or ultrasonography are indicated if synovial fluid cannot be obtained for analysis; findings of multiple linear or punctate calcification in articular cartilage, especially fibrocartilages, support the diagnosis but do not exclude gout or infection. Typical ultrasonographic findings of gout (double contour sign) may simulate findings of Ca pyrophosphate crystal deposits.
The prognosis for individual attacks of acute CPPD crystal deposition disease is usually excellent. However, chronic arthritis can occur, and severe destructive arthropathy resembling neurogenic arthropathy (Charcot joints) occasionally occurs.
Symptoms of acute synovial effusion abate with synovial fluid drainage and instillation of a microcrystalline corticosteroid ester suspension into the joint space (eg, 40 mg prednisolone acetate or prednisolone tertiary butylacetate into a knee).
Asymptomatic chondrocalcinosis becomes common with age, particularly in the knee, hip, wrist, anulus fibrosus, and symphysis pubis.
Arthritis can affect the knee and large peripheral joints and mimic other forms of arthritis.
Examine joint fluid for characteristic rhomboid- or rod-shaped crystals in synovial fluid that are not birefringent or are weakly positively birefringent, and exclude joint infection.
For acute symptoms, treat with an intra-articular corticosteroid or an oral NSAID.
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