What are the diagnostic criteria for pseudo gout?

Diagnosis of Pseudogout

The definitive diagnosis of pseudogout requires identification of calcium pyrophosphate dihydrate (CPPD) crystals in synovial fluid through joint aspiration and polarized light microscopy examination. 1

Diagnostic Approach

Step 1: Synovial Fluid Analysis (Gold Standard)

• Joint aspiration and synovial fluid analysis is the reference standard for diagnosing pseudogout
• CPPD crystals appear as:
  • Weakly positive birefringent (blue when parallel to the slow axis of the compensator)
  • Rhomboid or rod-shaped crystals
  • Shorter and broader than urate crystals

Step 2: Radiographic Findings

When joint aspiration is not feasible or inconclusive, radiographic evidence can support the diagnosis:

• Plain Radiography (first-line imaging):

  • Look for chondrocalcinosis (calcification in hyaline cartilage and fibrocartilage)
  • Common sites: radiocarpal joints, metacarpophalangeal joints, patellofemoral joints, and atlantoaxial joints 1
  • Also affects triangular fibrocartilage of wrists, menisci of knees, symphysis pubis, and labrum at pelvis

• Ultrasound (83% sensitivity, 76% specificity):

  • Intra-articular microtophi
  • Echogenic synovial hypertrophy
  • "Double contour sign" 1

• CT Scan:

  • Can identify chondrocalcinosis
  • Calcification of tendons, ligaments, and joint capsules
  • Osseous changes related to pseudogout 1

Step 3: Clinical Features

When crystal identification is not possible, consider these clinical characteristics:

• Acute monoarticular or oligoarticular arthritis
• Knee is most commonly affected joint (90.9% of cases in prosthetic joints) 2
• Pain (100% of cases), joint swelling (88.9%), decreased range of motion (100%), redness (33.3%), and fever (22.2%) 2
• More common in elderly patients
• May present as polyarticular involvement affecting 4 or more joints across different regions 1

Associated Conditions to Screen For

Pseudogout is associated with several metabolic conditions that should be evaluated:

• Primary hyperparathyroidism (3x higher risk in pseudogout patients) 1
• Hemochromatosis 1
• Hypomagnesemia (can trigger attacks) 1
• Chronic renal failure (3.7% incidence of chondrocalcinosis in dialysis patients, increasing to 15.8% in patients over 60) 3

Differential Diagnosis

• Gout: Differentiated by monosodium urate crystals (negatively birefringent) vs. CPPD crystals (weakly positive birefringent)
• Septic arthritis: Critical to rule out, especially with fever and acute monoarticular arthritis
• Rheumatoid arthritis: More symmetric, different joint distribution
• Osteoarthritis: Less acute presentation, different radiographic findings

Common Pitfalls in Diagnosis

1. Misdiagnosis as infection: Pseudogout can mimic prosthetic joint infection or spinal discitis/epidural abscess 2, 4
2. Premature antibiotic administration: 45.5% of patients receive antibiotics prior to joint aspiration, potentially leading to antibiotic overuse 2
3. Atypical presentations: Can present with skip lesions throughout the spine or with more diffuse calcification than typical linear stippled pattern in chronic renal failure 3, 4
4. Overlooking underlying metabolic disorders: Failure to screen for associated conditions like hyperparathyroidism, hemochromatosis, or hypomagnesemia

Diagnostic Algorithm

1. Acute joint pain/swelling → Joint aspiration with polarized microscopy
2. If aspiration not possible or inconclusive → Radiographic imaging (X-ray first, then ultrasound or CT if needed)
3. Screen for associated metabolic conditions (calcium, phosphate, magnesium, iron studies, PTH, renal function)
4. Consider alternative diagnoses if both crystal analysis and imaging are negative

Remember that pseudogout can have various clinical presentations beyond the classic acute arthritis ("pseudogout attack"), including chronic arthropathy resembling osteoarthritis and even asymptomatic chondrocalcinosis discovered incidentally on imaging.