How to diagnose Acute Intermittent Gout (AIG)?

Diagnosis of Acute Intermittent Gout (AIG)

Synovial fluid analysis with polarized light microscopy to identify monosodium urate (MSU) crystals is the gold standard for diagnosing acute gout and should be performed when diagnostic testing is necessary in patients with suspected acute gout. 1, 2

Primary Diagnostic Approach

Synovial Fluid Analysis

• Perform joint aspiration and synovial fluid analysis when:

  • The joint can be aspirated without substantial patient discomfort
  • An experienced clinician is available to minimize infection risk
  • A reliable source with polarizing microscope and trained operator is available
  • The clinical situation is ambiguous
  • There is significant probability of infection 1

• Look for:

  • Needle-like MSU crystals showing strong negative birefringence under polarized microscopy 3
  • White blood cell count (typically elevated in acute gout)

When Synovial Fluid Analysis Is Not Feasible

Clinical judgment may be appropriate when:

• The situation is less clinically ambiguous
• There is low probability of infection
• Typical presentation exists (e.g., podagra with appropriate risk factors) 1

Clinical Features to Evaluate

• Joint involvement pattern:

  • First metatarsophalangeal joint (50% of initial attacks)
  • Ankle, midtarsal, knee, wrist, finger, or elbow 2, 3
  • Monoarticular presentation (most common in early disease)
  • Rapid onset of severe pain and swelling
  • Erythema over the affected joint 2

• Patient characteristics:

  • Male gender (higher risk)
  • History of previous similar acute arthritis episodes
  • Associated cardiovascular diseases 2

• Risk factors:

  • Hyperuricemia (though not diagnostic on its own)
  • Obesity, hypertension
  • Medications: diuretics, low-dose aspirin, cyclosporine, tacrolimus
  • Alcohol consumption (particularly beer and spirits)
  • Diet rich in meat, shellfish, and fructose-rich foods/beverages 2
  • Comorbidities: chronic kidney disease, ischemic heart disease, heart failure, diabetes, dyslipidemia 2

Alternative Diagnostic Tools

Validated Clinical Prediction Rules

When synovial fluid analysis isn't possible, consider using:

• Janssens diagnostic rule (sensitivity 73-96%, specificity 47-86%)
• Clinical Gout Diagnosis criteria (sensitivity 97%, specificity 96%) 2

Imaging Techniques

• Ultrasound: Look for double contour sign (sensitivity 37-78%, specificity 64-97%) 2
• Dual-energy CT (DECT): High sensitivity (85-100%) and specificity (83-92%), but less sensitive in recent-onset acute gout 2
• Plain radiographs: Limited value for acute gout but may show erosions in chronic disease 2, 4

Laboratory Tests

• Serum uric acid: Often elevated but has poor sensitivity and specificity (53-61%) and should not be used alone for diagnosis 2, 5

Differential Diagnosis

Always consider other conditions that may mimic gout:

• Septic arthritis (critical to rule out)
• Rheumatoid arthritis
• Psoriatic arthritis
• Inflammatory episodes of osteoarthritis
• Calcium pyrophosphate deposition disease (pseudogout) 2, 6

Common Pitfalls to Avoid

• Relying solely on serum uric acid levels: Hyperuricemia alone is insufficient for diagnosis as it has poor sensitivity and specificity 2
• Delaying treatment: Early intervention improves outcomes; treatment should not be delayed 2
• Missing septic arthritis: Always consider infection in the differential diagnosis 2
• Overlooking atypical presentations: Oligoarticular or polyarticular presentations can mimic other inflammatory arthritides 6
• Neglecting comorbidities: Patients with gout often have significant cardiovascular and metabolic comorbidities that affect management 3

Remember that acute gout is characterized by recurrent attacks of synovitis, while chronic gout involves inflammatory and structural changes that may lead to persistent symptoms and tophi formation 3.