How to diagnose gouty arthritis?

Diagnosis of Gouty Arthritis

The definitive diagnosis of gouty arthritis requires identification of monosodium urate (MSU) crystals through synovial fluid aspiration and examination under polarized light microscopy, which is the gold standard diagnostic approach. 1, 2

Diagnostic Algorithm

Step 1: MSU Crystal Identification (Gold Standard)

• Perform synovial fluid aspiration and examination for MSU crystals in any patient with undiagnosed inflammatory arthritis 1
• MSU crystals appear as needle-shaped, negatively birefringent crystals under polarized microscopy 2
• This method has high sensitivity (84%) and extremely high specificity (100%) 2

Step 2: Clinical Diagnosis (When Crystal Identification Not Feasible)

When synovial fluid analysis is not possible, assess for these highly suggestive clinical features:

• Monoarticular involvement of first metatarsophalangeal joint (podagra) or ankle 1
• Rapid onset of severe pain and swelling (reaching maximum within 6-12 hours) 3
• Presence of overlying erythema 1
• Previous similar acute arthritis episodes 1
• Male gender 1
• Associated cardiovascular diseases 1
• Presence of hyperuricemia 1

Step 3: Imaging (When Diagnosis Remains Uncertain)

• Ultrasound: First-line imaging option showing double contour sign at cartilage surfaces or detection of tophi not evident on clinical examination 1, 2
  • Sensitivity: 63-83%, Specificity: 76-92% 2
• Dual-energy CT (DECT): For detecting MSU crystal deposition in deeper tissues 1, 2
  • Sensitivity: 85-100%, Specificity: 83-92% 2
• Plain radiographs: Limited value for diagnosis of gout flare but can show evidence of MSU crystal deposition in chronic gout 1

Important Diagnostic Considerations

Serum Uric Acid Testing

• Do not diagnose gout based on hyperuricemia alone 1
• Serum uric acid may be normal during acute attacks in up to 40% of patients 2
• Hyperuricemia has low specificity for gout diagnosis 1, 2

Clinical Presentation Patterns

• Acute gouty arthritis typically presents with:
  • Sudden and severe joint pain 3, 4
  • First MTP joint involvement in 50% of initial attacks 5
  • Rapid development of symptoms reaching maximum within 24 hours 1
  • Overlying erythema 1

Risk Factor Assessment

Search for risk factors for chronic hyperuricemia in every person with suspected gout 1:

• Chronic kidney disease
• Overweight/obesity
• Medications (diuretics, low-dose aspirin, cyclosporine, tacrolimus)
• Excess alcohol consumption (particularly beer and spirits)
• Consumption of non-diet sodas, meat, and shellfish

Common Pitfalls and Caveats

1. Relying solely on serum uric acid levels: Hyperuricemia alone is insufficient for diagnosis as it has poor specificity 1, 2

2. Failing to consider comorbidities: Systematically assess for associated conditions including obesity, renal impairment, hypertension, ischemic heart disease, heart failure, diabetes, and dyslipidemia 1

3. Misdiagnosing septic arthritis: Septic arthritis can coexist with gout and requires immediate treatment 2

4. Not performing synovial fluid analysis when indicated: When clinical presentation is ambiguous or infection is suspected, synovial fluid analysis should be performed if possible 1

5. Starting treatment without confirming diagnosis: Treatment should not be initiated based solely on clinical presentation without proper diagnostic confirmation 2

By following this three-step diagnostic approach (crystal identification, clinical assessment, and imaging), clinicians can accurately diagnose gouty arthritis and initiate appropriate management to reduce morbidity and improve quality of life for patients with this common inflammatory arthritis.