What are the diagnostic criteria and treatment options for pseudogout (calcium pyrophosphate deposition disease)?

Pseudogout: Symptoms and Diagnosis

Pseudogout (calcium pyrophosphate deposition disease or CPPD) is diagnosed primarily through identification of calcium pyrophosphate crystals in synovial fluid and characteristic radiographic findings of chondrocalcinosis.

Clinical Presentation

• Pseudogout typically presents with acute attacks of pain, swelling, redness, and decreased range of motion in affected joints 1
• Unlike gout which commonly affects the first metatarsophalangeal joint, pseudogout more frequently affects larger joints such as knees, wrists, and shoulders 2
• Attacks may be triggered by trauma, surgery, or medical events such as ischemic heart disease 2
• Pseudogout is more common in older adults, with prevalence increasing dramatically after age 70 3
• The clinical presentation can mimic other conditions including gout, septic arthritis, and rheumatoid arthritis 4

Diagnostic Criteria

Gold Standard: Crystal Identification

• Synovial fluid aspiration and microscopic examination for calcium pyrophosphate crystals is the definitive diagnostic test for pseudogout 3
• Under compensated polarized light microscopy, calcium pyrophosphate crystals appear as weakly positive birefringent rhomboid-shaped crystals (in contrast to the strongly negative birefringent needle-shaped crystals of gout) 2
• If septic arthritis is in the differential diagnosis, joint aspiration for Gram stain and culture is essential 3

Imaging Findings

• Radiography should be the initial imaging method for suspected pseudogout 3
• The hallmark radiographic finding is chondrocalcinosis - calcification of cartilage in the form of linear or punctate deposits 3, 5
• Target sites to evaluate for fibrocartilage chondrocalcinosis include:
  • Triangular fibrocartilage of the wrists
  • Menisci of the knees
  • Symphysis pubis
  • Labrum at the pelvis 3
• Hyaline cartilage involvement may occur at any joint 3
• Characteristic osseous changes from associated arthropathy typically involve the radiocarpal, metacarpophalangeal, atlantoaxial, and patellofemoral joints 3
• Important caveat: Pseudogout can occur without radiographic evidence of chondrocalcinosis, particularly in the wrist where it may present with radiocarpal joint space narrowing, sclerosis, and subchondral cystic degeneration of carpal bones 6

Advanced Imaging

• Ultrasound can detect:
  • Intra-articular microtophi
  • Echogenic synovial hypertrophy
  • "Icing" of the cartilage (double contour sign) 3
  • Ultrasound outperforms radiography for chondrocalcinosis detection 3
• CT can identify:
  • Chondrocalcinosis
  • Calcification of tendons, ligaments, and joint capsules
  • Osseous changes related to pseudogout 3
• MRI (particularly gradient-recalled echo sequences) can complement radiography by showing:
  • Synovitis
  • Additional osseous findings 3

Differential Diagnosis

• Gout: Distinguished by identification of monosodium urate crystals rather than calcium pyrophosphate crystals 2
• Septic arthritis: Must be ruled out in any acute monoarthritis, especially with fever 1
• Rheumatoid arthritis: More symmetric, involves different joint distribution 4
• Osteoarthritis: Pseudogout should be considered in evaluating any patient with osteoarthritis occurring in an atypical distribution 4

Diagnostic Pitfalls and Caveats

• Pseudogout can present without radiographic evidence of chondrocalcinosis, making diagnosis challenging 6
• Antibiotics should not be administered before joint aspiration and culture if infection is suspected, as this may lead to false-negative cultures 1
• Pseudogout in the shoulder (acromioclavicular joint) may present with nonspecific shoulder pain, requiring careful assessment of radiographs with bright light to detect discal and capsular calcifications 5
• Pseudogout can mimic prosthetic joint infection in patients with joint arthroplasty 1
• The diagnosis of pseudogout should not be made solely on clinical grounds without crystal identification, as clinical features overlap significantly with other arthritides 3

Diagnostic Algorithm

1. Perform joint aspiration for synovial fluid analysis

   • Identify calcium pyrophosphate crystals under polarized light microscopy
   • Rule out infection with Gram stain and culture 3

2. If joint aspiration is not feasible or inconclusive:

   • Obtain radiographs to look for chondrocalcinosis and characteristic joint involvement 3
   • Consider ultrasound to detect microtophi and "icing" of cartilage 3

3. If diagnosis remains uncertain:

   • Consider advanced imaging (CT or MRI) 3
   • Evaluate for associated conditions that may predispose to CPPD (e.g., hyperparathyroidism, hemochromatosis) 4