How to diagnose gout in a patient with no kidney disease?

Diagnosing Gout in Patients Without Kidney Disease

The definitive diagnosis of gout requires identification of monosodium urate (MSU) crystals in synovial fluid or tophus aspirate using polarized light microscopy, but when this is not feasible, a clinical diagnosis can be made based on characteristic features combined with imaging findings. 1

Gold Standard: Synovial Fluid Analysis

• Joint aspiration with synovial fluid analysis for MSU crystals is the reference standard, with sensitivity and specificity approaching 100% when performed by experienced operators 1, 2
• MSU crystals appear as needle-shaped, negatively birefringent crystals under polarizing microscopy 2
• Synovial fluid aspiration should be performed in every patient with suspected gout when feasible, particularly for the first attack, when the diagnosis is uncertain, or when septic arthritis cannot be excluded 1
• Even when MSU crystals are identified, Gram stain and culture must still be performed as gout and septic arthritis can coexist 2

Clinical Diagnosis When Aspiration Not Feasible

When synovial fluid analysis cannot be performed, gout should be strongly suspected based on the following clinical features: 1

• Monoarticular involvement of the first metatarsophalangeal joint (podagra) - this has the highest diagnostic value with 96% sensitivity and 97% specificity 2
• Rapid onset of severe pain reaching maximum intensity within 24 hours 1, 2
• Erythema over the affected joint 1
• Previous similar acute arthritis episodes 1
• Male gender 1
• Associated cardiovascular diseases 1
• Hyperuricemia (though this alone cannot diagnose gout) 1

The ACR/EULAR clinical diagnostic criteria achieve 92% sensitivity and 89% specificity when imaging is included, or 85% sensitivity and 78% specificity without imaging 2

Critical Caveat About Hyperuricemia

• Hyperuricemia alone should NOT be used to diagnose gout - only 22% of patients with serum uric acid >9 mg/dL develop gout over 5 years 1, 2
• Approximately 10% of patients with acute gout have normal serum uric acid levels during an attack 2
• Hyperuricemia has only 53-61% specificity for gout diagnosis 2

Imaging When Diagnosis Uncertain

When clinical diagnosis is uncertain and crystal identification is not possible, imaging should be used to search for MSU crystal deposition: 1

Ultrasound (First-Line Imaging)

• The "double contour sign" on cartilage surfaces is highly specific for urate deposits, with 74% sensitivity and 88% specificity 1, 2
• Ultrasound can detect tophi not evident on clinical examination 1
• Always include the first metatarsophalangeal joint bilaterally in ultrasound examination, even if asymptomatic 2
• Ultrasound performs better in late disease (>2 years duration) with 63% sensitivity compared to 50% in early disease 2

Dual-Energy CT (Second-Line Imaging)

• DECT has 85-100% sensitivity and 83-92% specificity for detecting MSU crystal deposition 1, 2
• More expensive and involves radiation exposure 2
• Less sensitive in patients with shorter disease duration 2

Plain Radiographs

• Plain radiographs have limited value for diagnosing acute gout flares but can identify chronic changes and rule out alternative diagnoses 1, 2

Risk Factor Assessment

In every patient with suspected or confirmed gout, systematically assess for: 1

• Overweight/obesity (relative risk 3.81) 2
• Medications: diuretics (relative risk 1.72), low-dose aspirin, cyclosporine, tacrolimus 1, 2
• Excess alcohol consumption, particularly beer and spirits 1
• Diet high in meat, shellfish, and non-diet sodas 1
• Associated comorbidities: hypertension (relative risk 3.93), ischemic heart disease, heart failure, diabetes, dyslipidemia 1, 2

Diagnostic Algorithm

Step 1: Attempt synovial fluid aspiration for MSU crystal identification (gold standard) 1

Step 2: If aspiration not feasible, make clinical diagnosis based on:

• Podagra with rapid onset (<24 hours to maximum pain) 1
• Erythema and previous similar episodes 1
• Male gender and cardiovascular comorbidities 1
• Hyperuricemia (supportive but not diagnostic) 1

Step 3: If clinical diagnosis uncertain, use imaging:

• Start with ultrasound looking for double contour sign and tophi 1
• Consider DECT if ultrasound inconclusive and disease duration >2 years 2

Common Pitfalls to Avoid

• Do not diagnose gout based solely on hyperuricemia - up to 80% of patients with hyperuricemia never develop gout 2
• Do not exclude gout based on normal serum uric acid during an acute attack - 10% of acute gout patients have normal levels 2
• Do not rely on imaging alone - integrate patient history, physical examination, and laboratory findings 2
• Be aware that clinical algorithms have relatively low specificity, raising the risk of missing septic arthritis which has similar presentation 2
• Joint aspiration is technically difficult in smaller joints and rarely performed in primary care, but should still be attempted when diagnosis is uncertain 2