Epidemiology

• Age of onset: adults > 60 years

Etiology

• The primary (idiopathic) form is most common, with age as a major risk factor.
• Secondary forms
  • Joint trauma/damage: including joint surgery, previous juvenile idiopathic arthritis, and Osteoarthritis
  • Metabolic disorders: including hyperparathyroidism, hemochromatosis, hypomagnesemia, hypophosphatasia, and possibly gout
  • Familial chondrocalcinosis: due to mutations in the CCAL1 or CCAL2 genes

Pathophysiology

Deposition of calcium pyrophosphate dihydrate (CPP or CPPD) crystals in articular cartilage → paroxysmal joint inflammation and cartilage destruction → inflammatory arthritis (crystalline arthritis)

Clinical features

Acute CPP crystal arthritis (pseudogout)

• Clinical features
  • Acute attack of pain and swelling in the affected joint(s)
  • Monoarthritis (occasionally oligoarthritis)
  • Most commonly affects the knee and wrist; can also affect other large joints (e.g., hips, ankles)
  • Typically self-limited
• Features that differ from acute gout
  • Longer duration of acute attacks
    • Up to several months
  • Possible systemic symptoms
    • E.g., fever, chills, altered mental status in the elderly

Chronic CPP crystal arthritis

• Osteoarthritis-like presentation (osteoarthritis with CPPD; pseudo-osteoarthritis)
  • Most common form of CPPD disease
  • Characterized by progressive joint degeneration
    • Usually polyarticular; can occur in joints not typically affected by OA
    • More severe than typical OA
    • Often associated with pseudogout-like flares of acute inflammatory arthritis

Diagnostics

Arthrocentesis and synovial fluid analysis (SFA)

• Cloudy fluid
• Polarized light microscopy (with a red filter) appearance of CPP crystals (opposite to findings in Gout)
  • Rhomboid-shaped crystals that are weakly positively birefringent
  • Crystals appear blue when their optical axis is oriented parallel to the polarizer.
  • Crystals appear yellow when their axis is perpendicular to the polarizer.
• Cell count: WBC > 2000/μL with > 50% neutrophils

Imaging

• X-ray of the affected joint(s)
  • Chondrocalcinosis: calcification of cartilage in the affected joints

Treatment