Basic Calcium Phosphate Crystal Deposition Disease and Calcium Oxalate Crystal Deposition Disease

Most pathologic calcifications throughout the body contain mixtures of carbonate-substituted hydroxyapatite and octacalcium phosphate. Because these ultramicroscopic crystals are nonacidic calcium phosphates, the term basic calcium phosphate (BCP) is much more precise than apatite. These ultramicroscopic crystals occur in snowball-like clumps in rheumatic conditions (eg, calcific tendinitis, calcific periarthritis, some cases of progressive systemic sclerosis Systemic Sclerosis Systemic sclerosis is a rare chronic disease of unknown cause characterized by diffuse fibrosis and vascular abnormalities in the skin, joints, and internal organs (especially the esophagus... read more and dermatomyositis Autoimmune Myositis Autoimmune myositis is characterized by inflammatory and degenerative changes in the muscles (polymyositis, necrotizing immune-mediated myopathy) or in the skin and muscles (dermatomyositis)... read more ). They also occur in joint fluids and cartilages of patients with all degenerative arthropathies sufficiently advanced to cause joint space narrowing on x-ray.

BCP crystals can destroy joints and can cause severe intra-articular or periarticular inflammation.

Milwaukee shoulder/knee syndrome, a chronic destructive arthropathy affecting predominantly older women that usually develops in the shoulders and often knees, is one example. The syndrome is characterized by chronic large but minimally inflammatory synovial effusions.

Acute pseudo-podagra due to periarticular BCP deposition can mimic gout Gout Gout is a disorder caused by hyperuricemia (serum urate > 6.8 mg/dL [> 0.4 mmol/L]) that results in the precipitation of monosodium urate crystals in and around joints, most often causing recurrent... read more ; it occurs as a discrete syndrome in young women (less often in young men) and is treated the same as acute gout Treatment of acute flares Gout is a disorder caused by hyperuricemia (serum urate > 6.8 mg/dL [> 0.4 mmol/L]) that results in the precipitation of monosodium urate crystals in and around joints, most often causing recurrent... read more . The diagnostic fluffy or dense periarticular calcification present on radiographs during an acute flare may spontaneously resolve over weeks to months.

Besides synovial fluid analysis, x-rays should be taken of symptomatic joints. On x-ray, BCP crystals may be visible as periarticular cloudlike opacities; the crystals often spontaneously resolve over months or occasionally within days. Definitive assay for BCP crystals in synovial fluid is not readily available. Clumped crystals can usually be identified only with special calcium stains or transmission electron microscopy. The clumps are not birefringent under polarized light.

Treatment of BCP crystal deposition disease with oral colchicine, an NSAID, or, if a large joint is involved, intra-articular corticosteroid ester crystal suspension is helpful. Treatment is the same as that for acute gout Treatment of acute flares Gout is a disorder caused by hyperuricemia (serum urate > 6.8 mg/dL [> 0.4 mmol/L]) that results in the precipitation of monosodium urate crystals in and around joints, most often causing recurrent... read more .

Calcium oxalate crystal deposition is extremely rare. It occurs most often in azotemic patients receiving hemodialysis or peritoneal dialysis, particularly those treated with ascorbic acid (vitamin C), which is metabolized to oxalate. However, the evolution of dialysis exchange fluids has resulted in the virtual disappearance of this disease.

Crystals may deposit in blood vessel walls and skin, as well as joints. The crystals Microscopic Examination of Crystals in Joints appear as positively or indeterminately birefringent bipyramidal structures. Synovial fluid may have > 2000 white blood cells/mcL. On x-ray, calcium oxalate crystals are indistinguishable from BCP periarticular calcifications or calcium pyrophosphate dihydrate (CPPD) crystal deposits in cartilage.

Treatment of calcium oxalate crystal deposition disease is the same as that for calcium pyrophosphate arthritis (CPPD crystal deposition disease) Treatment Calcium pyrophosphate arthritis (CPP arthritis) involves intra-articular and/or extra-articular deposition of calcium pyrophosphate dihydrate (CPPD) crystals. Manifestations are protean and... read more .