Diagnosis of Tophi in Adults with Chronic Gout
Synovial fluid or tophus aspirate analysis demonstrating monosodium urate (MSU) crystals under polarized microscopy is the gold standard for diagnosing tophi, but clinical examination combined with imaging can establish the diagnosis when aspiration is not feasible. 1, 2
Gold Standard Diagnostic Approach
Aspirate and analyze tophi or synovial fluid for MSU crystals, which appear as needle-shaped, negatively birefringent crystals under polarizing microscopy with 85% sensitivity and 93% specificity. 2 This provides definitive diagnosis and should be performed when clinically feasible. 1
Critical Pitfall to Avoid
- Always perform Gram stain and culture even when MSU crystals are identified, as gout and septic arthritis coexist in 5-10% of cases. 2 Missing concurrent infection can lead to serious morbidity.
Clinical Diagnosis When Aspiration Not Feasible
When synovial fluid analysis cannot be performed, diagnose tophaceous gout clinically based on:
- Visible or palpable tophi (99% specificity, 30% sensitivity for gout diagnosis) 2
- History of recurrent acute arthritis episodes with rapid onset of severe pain 2
- Male gender and cardiovascular comorbidities (hypertension, ischemic heart disease) increase likelihood (odds ratio 2.5 for males) 2
This clinical approach achieves 75% sensitivity and 85% specificity. 2
Imaging Modalities for Uncertain Cases
Use dual-energy CT (DECT) or ultrasound when clinical diagnosis is uncertain and crystal identification is not possible. 2
DECT Imaging
- Achieves 85-100% sensitivity and 83-92% specificity for detecting MSU crystal deposition 2
- Particularly useful for detecting tophi in atypical locations 3
Ultrasound Imaging
- Look for the "double contour sign" on cartilaginous surfaces, which is 95% specific for urate deposits 2
- Can detect tophaceous deposits over joints (e.g., olecranon fossa) 4
Essential Baseline Assessment
Once tophi are diagnosed, systematically evaluate:
- Serum uric acid level (typically elevated, mean baseline ~10 mg/dL in tophaceous disease) 5
- Renal function (chronic kidney disease has odds ratio of 2.2 for gout) 2
- Cardiovascular risk factors (obesity present in 60%, hypertension in 40% of gout patients) 2
- Medication review for drugs inducing hyperuricemia (especially diuretics) 1, 6
- Extent of disease burden: document number, size, and location of tophi on physical examination 1
Recognition of Atypical Presentations
Be vigilant for tophi in unusual locations, as they can present as the first sign of gout even without prior joint symptoms:
- Head and neck, skin (disseminated gout nodulosis), middle ear 4, 7, 3
- Spine, bones, tendons, ligaments, nerves 3
- Transplant recipients, women, and elderly patients are particularly susceptible to developing tophi 3
- Tophi can mimic infection, malignancy, or other connective tissue diseases 3
Treatment Implications of Diagnosis
Once tophaceous gout is diagnosed, initiate urate-lowering therapy (ULT) immediately with a target serum urate <6 mg/dL. 1, 2 This is an absolute indication for pharmacologic ULT regardless of flare frequency. 1
- For severe tophaceous disease with multiple tophi, target serum urate <5 mg/dL to achieve faster tophus regression (70% reduction at 1 year vs. 50% at 2 years with <6 mg/dL target). 2
- After complete tophus resolution, maintain serum urate <6 mg/dL indefinitely 1, 2
Monitoring Strategy
- Check serum urate every 2-5 weeks during dose titration until target achieved 8
- Measure tophus size at each visit to track treatment response 8
- Continue lifelong monitoring to maintain target 8
When to Refer to Rheumatology
Refer patients with tophi to a rheumatologist when: