What is the appropriate diagnosis and treatment for an elderly male with recurrent knee swelling and pain, initially in the left knee and then in the right knee?

Migratory Inflammatory Arthritis: Suspect Crystal Arthropathy or Infection

The clinical presentation of knee swelling and pain that "stopped and started again" in the contralateral knee strongly suggests a migratory inflammatory arthritis, most commonly crystal-induced arthropathy (gout or pseudogout) or, less commonly, septic arthritis—both require urgent joint aspiration for definitive diagnosis. 1, 2

Immediate Diagnostic Approach

Joint Aspiration is Essential

• Perform arthrocentesis of the currently affected (right) knee immediately to analyze synovial fluid for:

  • Cell count and differential (septic arthritis typically >50,000 WBC/mm³ with >90% neutrophils) 3, 4
  • Crystal analysis under polarized microscopy (negatively birefringent needle-shaped crystals for gout; positively birefringent rhomboid crystals for pseudogout) 5, 3
  • Gram stain and culture to exclude infection 3, 4

• Aspiration can be performed under ultrasound or fluoroscopic guidance if an effusion is present 5

Initial Imaging

• Obtain AP and lateral radiographs of both knees to evaluate for:

  • Chondrocalcinosis (suggests pseudogout/CPPD) 5
  • Erosive changes or tophi (chronic gout) 1, 2
  • Osteophytes or joint space narrowing (osteoarthritis as alternative diagnosis) 5, 1
  • Subchondral bone changes 5

• Radiographs should precede advanced imaging in this acute presentation 5, 6

Critical Differential Diagnoses

Crystal Arthropathy (Most Likely)

• Gout presents with acute monoarticular arthritis that can migrate between joints, classically affecting the knee in elderly patients 1, 2
• Pseudogout (CPPD) similarly causes acute inflammatory monoarthritis with migratory pattern, more common in elderly males 5, 1
• The "stop-start" pattern with contralateral involvement is classic for crystal disease 3

Septic Arthritis (Must Exclude)

• Fever, erythema, warmth, and severe pain with limited range of motion suggest infection 4, 7
• Any suspicion of infection requires urgent aspiration and empiric antibiotics pending culture results 3, 4
• Septic arthritis can rarely present with sequential joint involvement 3

Other Inflammatory Arthropathies

• Reactive arthritis or other seronegative spondyloarthropathies can cause migratory oligoarthritis 1, 2
• Rheumatoid arthritis typically presents with symmetric polyarthritis, not sequential monoarthritis 3

Treatment Algorithm

If Crystal Arthropathy Confirmed

• For acute gout flare:

  • NSAIDs (if no contraindications), colchicine, or corticosteroids for acute inflammation 8
  • Do NOT initiate allopurinol during acute attack—wait until inflammation resolves, then start at 100 mg daily and titrate weekly by 100 mg increments to achieve serum uric acid <6 mg/dL 8
  • Continue anti-inflammatory prophylaxis (colchicine or NSAIDs) for several months when initiating urate-lowering therapy 8

• For pseudogout:

  • NSAIDs, colchicine, or intra-articular/systemic corticosteroids 5, 3
  • No specific urate-lowering therapy available 5

If Septic Arthritis Confirmed

• Urgent orthopedic consultation for surgical drainage 3, 4
• Empiric IV antibiotics immediately after cultures obtained 3, 4

If Diagnosis Remains Unclear After Aspiration

• Consider MRI without IV contrast if radiographs are normal and aspiration is non-diagnostic, to evaluate for:

  • Occult fractures or bone marrow edema 5, 1
  • Meniscal pathology or ligamentous injury 5, 6
  • Synovitis or effusion characterization 5

• Ultrasound with power Doppler can demonstrate synovial blood flow and effusions, useful for guiding repeat aspiration 5

Common Pitfalls to Avoid

• Never attribute migratory knee pain solely to osteoarthritis without excluding crystal disease or infection—OA does not migrate between joints 1, 2, 6

• Do not rely on serum uric acid levels during acute presentation—levels can be normal or even low during acute gout flares 8

• Avoid premature MRI before obtaining radiographs and attempting aspiration—approximately 20% of patients with chronic knee pain undergo MRI without recent radiographs, leading to unnecessary costs 5, 1

• Consider referred pain from hip or lumbar spine if knee examination and imaging are unremarkable, though less likely with bilateral sequential involvement 1, 2, 9

• Do not start allopurinol during acute gout attack—this can paradoxically worsen or prolong the flare 8