What are the diagnostic steps and treatment options for pseudogout?

Diagnosing Pseudogout

X-ray imaging of the affected joint is the primary diagnostic method for pseudogout, showing characteristic chondrocalcinosis in fibrocartilage and hyaline cartilage. 1

Definitive Diagnosis

The definitive diagnosis of pseudogout (calcium pyrophosphate dihydrate deposition disease or CPPD) requires:

1. Joint fluid aspiration and crystal analysis:

   • Identification of calcium pyrophosphate dihydrate (CPPD) crystals in synovial fluid
   • Examination under compensated polarized light microscopy
   • CPPD crystals appear weakly positive birefringent (blue when parallel to the slow axis of the red compensator) and rhomboid-shaped 2, 3

2. Radiographic findings:

   • Chondrocalcinosis (calcification in cartilage)
   • Target sites to evaluate include:
     • Triangular fibrocartilage of the wrists
     • Menisci of the knees
     • Symphysis pubis and labrum at the pelvis
     • Hyaline cartilage at any joint 1

Diagnostic Algorithm

1. Clinical presentation:

   • Acute or chronic joint pain
   • Often affects larger joints (unlike gout which typically affects the first MTP joint)
   • May follow trauma, surgery, or ischemic heart disease 2
   • May mimic gout or other inflammatory arthritis

2. Initial imaging:

   • X-ray of affected area (rated 9/9 for appropriateness) 1
   • Look for:
     • Soft tissue calcification in fibrocartilage and hyaline cartilage
     • Characteristic arthropathy involving radiocarpal, metacarpophalangeal, atlantoaxial, and patellofemoral joints 1

3. Confirmatory testing:

   • Joint aspiration for crystal analysis (gold standard)
   • Identification of rhomboid-shaped, weakly positive birefringent CPPD crystals under compensated polarized light microscopy 2, 3

4. Additional imaging (if needed):

   • Ultrasound (rated 5/9 for appropriateness) 1

     • Can detect intra-articular microtophi
     • Shows echogenic synovial hypertrophy
     • "Icing" of cartilage (double contour sign)

   • CT without contrast (rated 5/9 for appropriateness) 1

     • Can identify chondrocalcinosis and calcification of tendons, ligaments, and joint capsules
     • Shows characteristic osseous changes

   • MRI without contrast (rated 5/9 for appropriateness) 1

     • Can show synovitis and additional osseous findings
     • Gradient-recalled echo MRI outperforms radiography for chondrocalcinosis detection

Differential Diagnosis

Key conditions to distinguish from pseudogout:

1. Gout:

   • Monosodium urate crystals (strongly negative birefringent) vs. CPPD crystals (weakly positive birefringent)
   • Different joint distribution (gout often affects first MTP joint) 2

2. Septic arthritis:

   • Must be ruled out in acute presentations
   • Gram stain and culture of synovial fluid should be performed even if CPPD crystals are identified 4

3. Osteoarthritis:

   • May coexist with pseudogout
   • Lacks crystal deposition on microscopy 5

Common Pitfalls and Caveats

1. Misdiagnosis: Pseudogout can be misdiagnosed as gout, septic arthritis, or osteoarthritis. Always confirm with crystal analysis 2

2. Atypical presentations:

   • May occur in younger patients with chronic renal failure 6
   • Can present with more diffuse calcification than the usual linear stippled pattern in renal failure patients 6
   • Can affect unusual joints like the elbow or temporomandibular joint 6, 3

3. Secondary causes: Consider underlying conditions that may precipitate pseudogout:

   • Hyperparathyroidism and post-parathyroidectomy (hungry bone syndrome) 7
   • Chronic renal failure (3.7% incidence, increasing to 15.8% in patients over 60) 6
   • Trauma, surgery, or ischemic heart disease 2

4. Crystal identification challenges: Some other crystals (calcium oxalate, synthetic steroids, EDTA) are also birefringent. Quantitative analysis or observation of crystal structure in calcified sections may be needed for definitive diagnosis 3

By following this diagnostic approach, clinicians can accurately diagnose pseudogout and distinguish it from other crystal arthropathies and inflammatory joint conditions.