How is tophi in gout diagnosed and treated?

Diagnosis and Management of Tophi in Gout

The definitive diagnosis of tophi in gout requires identification of monosodium urate (MSU) crystals through aspiration of the tophus and examination under polarized light microscopy, revealing characteristic needle-shaped negatively birefringent crystals. 1, 2

Diagnostic Approach to Tophi

Clinical Diagnosis

• Tophi appear as firm, painless or painful nodules in periarticular tissues, tendons, bursae, or subcutaneous tissues
• Common locations include:
  • First metatarsophalangeal joints
  • Fingers
  • Elbows
  • Knees
  • Achilles tendons
  • Ears

Confirmatory Testing

1. Fine needle aspiration of tophus - Gold standard 1, 3

   • Reveals characteristic needle-shaped MSU crystals
   • Crystals appear negatively birefringent under polarized microscopy
   • High sensitivity (84%) and extremely high specificity (100%) 2

2. Imaging modalities when crystal identification is not feasible 1:

   • Ultrasound (US) - First-line imaging option

     • Double contour sign: sensitivity 63-83%, specificity 76-92% 1
     • Tophus visualization: sensitivity 65%, specificity 80% 1

   • Dual-energy CT (DECT)

     • Sensitivity 85-100%, specificity 83-92% 1
     • Useful for detecting MSU crystal deposition in deeper tissues
     • Limited by availability and radiation exposure 1

   • Conventional radiography

     • Limited value in early disease
     • May show erosions with overhanging edges in chronic tophaceous gout
     • More useful for differential diagnosis than confirmation 1

Management of Tophi

Pharmacological Treatment

1. Urate-Lowering Therapy (ULT) - Primary treatment 1

   • Target serum urate level:

     • <6 mg/dL (0.36 mmol/L) as minimum target 1
     • <5 mg/dL (0.30 mmol/L) for faster tophi resolution 1, 4, 5

   • First-line ULT options:

     • Allopurinol: Start at low dose (50-100 mg) and titrate upward 1
     • Febuxostat: Alternative when allopurinol is not tolerated 1
     • Probenecid or benzbromarone (uricosurics): Alternative first-line agents 1

   • For refractory cases:

     • Combination therapy (XOI + uricosuric agent) 1
     • Pegloticase: For severe tophaceous gout refractory to oral ULT 1, 6
       • Complete resolution of at least one target tophus in 45% of patients receiving biweekly infusions vs 8% with placebo 6
       • Higher risk of infusion reactions 6, 4

Monitoring Treatment Response

• Regular measurement of serum urate levels
• Clinical assessment of tophi size and number
• Ultrasound or DECT may be used to monitor tophi regression 1
• The velocity of tophi reduction is directly related to how low serum urate levels are maintained 5

Surgical Management

• Surgery is indicated only in selected cases 1:
  • Nerve compression
  • Mechanical impingement
  • Infection
  • Severe deformity affecting function

Important Clinical Considerations

Comorbidity Screening

Patients with tophi should be assessed for associated conditions 1:

• Chronic kidney disease
• Hypertension
• Ischemic heart disease
• Heart failure
• Diabetes
• Dyslipidemia
• Obesity

Common Pitfalls to Avoid

1. Relying solely on serum uric acid for diagnosis (may be normal during acute attacks in up to 40% of patients) 2
2. Failing to rule out infection when diagnosing gout (septic arthritis can coexist with gout) 2
3. Inadequate ULT dosing - insufficient to achieve target serum urate levels
4. Discontinuing ULT after tophi resolution (treatment should be continued indefinitely) 1
5. Failing to provide prophylaxis against acute flares when initiating ULT

Prognosis

• Tophi can lead to joint destruction, deformity, and functional impairment if left untreated 7, 8
• Effective ULT leads to gradual resolution of tophi over months to years 5
• Lower serum urate levels correlate with faster tophi resolution 5
• Chronic tophaceous gout is associated with increased mortality risk 8

By following this structured approach to diagnosis and management, clinicians can effectively identify and treat tophi in gout, preventing complications and improving patient outcomes.