General
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• Also called pseudogout, chondrocalcinosis
• Common finding in arthritic joints

Pathophysiology
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• Calcium pyrophosphate dehydrate (CPPD) crystals develop first in menisci and intervertebral discs, may seed the joint and elicit neutrophilic response (Hum Path 1995;26:587)
• 50% get significant joint damage
• CPPD deposition may also cause symptoms similar to septic arthritis, polyarticular inflammatory arthritis or degenerative osteoarthritis

Diagrams
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Pathogenesis

Sites
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• Knee is common site; 50% have involvement of several joints at diagnosis

Clinical features
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• Age 50+ years, 30% of patients are at least 85 years old
• Hereditary variant: symptoms early in life, associated with severe osteoarthritis
• Secondary: associated with prior joint damage, hyperparathyroidism, hemochromatosis, hypomagnesemia, hypothyroidism, ochronosis, diabetes mellitus

Diagnosis
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• Radiographic or microscopic detection of CPPD crystals
• Ultrasound is very sensitive (Ann Rheum Dis 2005;64:638)

Laboratory
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• Synovial fluid has high white count (2000-8000 cells/mm3), 80% neutrophils with intracellular crystals; later mononuclear cells with intra- or extracellular crystals

Radiology images
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Pyrophosphate arthropathy

Meniscal chondrocalcinosis

Case reports
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• 65 year old woman with crystal deposition in knee (Arch Pathol Lab Med 2001;125:705)
• 78 year old woman with pseudogout at craniocervical junction (Arch Pathol Lab Med 2003;127:895)
• Massive total body disease, including vertebral disks (Arch Pathol Lab Med 1982;106:352)

Treatment
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• Supportive (Ther Adv Musculoskelet Dis 2012;4:121)

Gross description
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• Chalky white deposits in articular tissue

Micro description
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• Small rectangular (rhomboid) crystals that are weakly positive birefringent; may have histiocytic and giant cell reaction around these crystals
• CPPD crystals have rhomboid or parallelelipedic morphology

Micro images
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H&E (A-C), Shiddam staining (figure 2)

High magnification

Compensated polarised light microscopy

H&E, polarized light

Differential diagnosis
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• Crystal deposition: gout, deposition of calcium phosphate, talc, methyl methacrylate (prosthetic joints)

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