What is the diagnostic approach for gout in an adult (typically men >40) presenting with sudden severe mono‑articular arthritis of the first metatarsophalangeal joint?

How to Diagnose Gout

Joint aspiration with synovial fluid analysis demonstrating needle-shaped, negatively birefringent monosodium urate (MSU) crystals under polarized light microscopy is the definitive diagnostic test for gout, achieving sensitivity and specificity approaching 100%. 1, 2, 3

When Joint Aspiration is Mandatory

• Perform arthrocentesis whenever septic arthritis cannot be clinically excluded, as gout and bacterial infection can coexist—even when MSU crystals are identified, Gram stain and culture must be performed. 1, 2
• Aspiration is required for first suspected gout attacks, atypical presentations (polyarticular involvement, unusual joint distribution, systemic symptoms including fever), or when diagnosis remains uncertain after clinical assessment. 1, 3
• MSU crystals appear as needle-shaped with strong negative birefringence under polarizing microscopy and can be detected in approximately 70% of patients even during intercritical periods. 1, 4

Clinical Diagnosis Algorithm (When Aspiration Not Feasible)

When joint aspiration cannot be performed, validated clinical algorithms achieve >80% sensitivity and specificity for gout diagnosis. 1, 2

High-Value Clinical Features:

• Podagra (first metatarsophalangeal joint involvement) has the highest diagnostic value with sensitivity 96%, specificity 97%, and likelihood ratio 30.64. 1
• Rapid pain onset reaching maximum intensity within 6-24 hours is characteristic of crystal inflammation. 1, 5, 6
• Erythema over the affected joint significantly increases likelihood of gout. 1, 3
• History of prior similar attacks is a strong supporting feature. 1, 3
• Male gender and cardiovascular comorbidities raise pre-test probability. 1, 3

ACR/EULAR 2015 Classification Criteria:

• A score ≥8 points is diagnostic with sensitivity 92% and specificity 89% (with imaging) or sensitivity 85% and specificity 78% (without imaging). 1, 2, 3
• Key high-scoring features include presence of tophi (odds ratio 7.29), resolution of pain within 2 weeks (odds ratio 3.58), and double contour sign on ultrasound (odds ratio 7.23). 3

Imaging Modalities

First-Line: Ultrasound

• Ultrasound is the recommended initial imaging modality when clinical diagnosis is uncertain, with the "double contour sign" on cartilage surfaces having sensitivity 74% and specificity 88%. 7, 1, 2
• Always scan the first metatarsophalangeal joint bilaterally, even if asymptomatic, as this is the disease-specific target site. 7, 1
• Ultrasound detects tophi with 65% sensitivity and 80% specificity, appearing as hyperechoic masses with a "wet clumps of sugar" appearance. 1
• Ultrasound sensitivity is significantly lower in early disease (<2 years) at only 50% versus 63% in late disease, and it can also assess inflammation unlike DECT. 1

Second-Line: Dual-Energy CT (DECT)

• DECT should be considered when ultrasound is negative but clinical suspicion remains high, particularly in patients with disease duration >2 years. 7, 1, 2
• DECT has sensitivity 85-100% and specificity 83-92% for detecting MSU crystal deposition. 7, 1, 2, 3
• DECT is less sensitive in patients with shorter history of flares and early disease. 1, 3

Limited Role: Plain Radiography

• Plain radiographs are useful only for assessing chronic structural damage or excluding alternative diagnoses and should not be the primary diagnostic modality for acute gout. 1, 8, 9
• Radiographs are frequently normal in early or acute gout, showing at most nonspecific soft-tissue swelling. 1, 9

Laboratory Testing

Serum Uric Acid:

• Hyperuricemia alone cannot diagnose gout and normal levels do not exclude it—approximately 10% of patients with acute gout have normal serum uric acid during an attack because uric acid behaves as a negative acute phase reactant during inflammation. 1, 3
• Only 22% of asymptomatic individuals with serum uric acid >9 mg/dL develop gout within 5 years. 1
• Serum uric acid has limited diagnostic value during acute attacks but is essential for long-term management decisions. 1

24-Hour Urinary Uric Acid:

• Measure in selected patients with early-onset gout (<25 years), family history of young-onset gout, or history of renal calculi to identify urate overproducers versus underexcretors. 1

Risk Factor and Comorbidity Assessment

Systematically evaluate the following risk factors and comorbidities: 1, 2, 3

Risk Factor/Comorbidity	Relative Risk
Chronic kidney disease	4.95
Hypertension	3.93
Obesity	3.81
Diuretic use	1.72

• Screen for renal impairment, ischemic heart disease, heart failure, diabetes mellitus, and dyslipidemia, which frequently coexist with gout. 1, 2, 3
• Assess alcohol consumption (particularly beer), diet high in meat/shellfish, and high-fructose corn syrup consumption. 1, 3, 8
• Review medications including diuretics, low-dose aspirin, cyclosporine, and tacrolimus. 1, 3

Practical Diagnostic Algorithm

Step 1: If septic arthritis cannot be excluded, fever is present, or this is the first suspected gout attack, perform joint aspiration with crystal analysis, Gram stain, and culture. 1, 2, 3

Step 2: If classic podagra with typical features (rapid onset, erythema, no fever, multiple risk factors) is present and infection is unlikely, diagnose gout clinically using validated criteria. 1, 3

Step 3: If clinical diagnosis is uncertain and aspiration is not feasible, obtain ultrasound of symptomatic joints plus bilateral first MTP joints. 7, 1, 2

Step 4: If ultrasound is negative but suspicion remains high—particularly in disease >2 years—consider DECT to detect MSU crystal deposition. 7, 1, 2

Step 5: If all testing is inconclusive, refer to rheumatology for expert evaluation. 2

Critical Pitfalls to Avoid

• Never diagnose gout based on hyperuricemia alone—up to 80% of patients with hyperuricemia never develop gout. 1
• Never exclude septic arthritis based solely on clinical appearance—if infection cannot be ruled out clinically, joint aspiration with Gram stain and culture is mandatory regardless of gout suspicion. 1, 2
• Do not rely on imaging alone—patient history, physical examination, and laboratory findings must be integrated into the diagnostic assessment. 7, 1
• All imaging must be performed and interpreted by trained healthcare professionals to ensure accuracy. 7, 1
• Imaging abnormalities related to crystal deposition may not always correlate with clinical manifestations, with 15-25% of people with asymptomatic hyperuricemia having asymptomatic MSU crystal deposition. 1