Hyperuricemia - Gout

Indications for Testing

• Swollen, erythematous joint(s)

Criteria for Diagnosis

• Diagnosis based on new guidelines (ACR/EULAR, 2015)
  • Step 1: Sufficient criterion (if met, can classify as gout)
    • Presence of MSU crystals in a symptomatic joint or bursa (i.e., in synovial fluid) or tophus
  • Step 2: The ACR/EULAR gout classification criteria
    • Entry criterion – at least 1 episode of swelling, pain, or tenderness in a peripheral joint or bursa
    • Score of 8 confirms gout
    • ACR-EULAR gout classification criteria and scoring

      ACR/EULAR Gout Classification Criteria*
      Criteria	Categories	Score
      Clinical Pattern of joint/bursa involvement during symptomatic episode(s) ever**	Ankle or midfoot Involvement of the first metatarsophalangeal joint	1 2
      Characteristics of symptomatic episode(s) ever Erythema overlying affected joint (patient- reported or physician-observed) Can't bear touch or pressure to affected joint Great difficulty with walking or inability to use affected joint	One characteristic Two characteristics Three characteristics	1 2 3
      Time course of episode(s) ever Presence (ever) of ≥2, irrespective of antiinflammatory treatment Time to maximal pain <24 hours Resolution of symptoms in ≤14 days Complete resolution (to baseline level) between symptomatic episodes	One typical episode Recurrent typical episodes	1 2
      Clinical evidence of tophus	Present	4
      Laboratory Serum urate         Synovial fluid analysis of a symptomatic (ever) joint or bursa	<4 mg/dl (<0.24 mmoles/liter)*** 6–<8 mg/dl (0.36–<0.48 mmoles/liter) 8–<10 mg/dl (0.48–<0.60 mmoles/liter) ≥10 mg/dl (≥0.60 mmoles/liter)   MSU negative	-4 2 3 4   -2
      Imaging **** Imaging evidence of urate deposition in symptomatic (ever) joint or bursa Imaging evidence of gout-related joint damage	Present   Present	4   4
      * A web-based calculator can be accessed at: http://goutclassificationcalculator.auckland.ac.nz, and through the American College of Rheumatology (ACR) and European League Against Rheumatism (EULAR) web sites. **Symptomatic episodes are periods of symptoms that include any swelling, pain, and/or tenderness in a peripheral joint or bursa. ***If serum urate level is <4 mg/dl (<0.24 mmoles/liter), subtract 4 points; if serum urate level is ≥4−<6 mg/dl (≥0.24−<0.36 mmoles/liter), score this item as 0. **** If imaging is not available, score these items as 0.

Laboratory Testing

• Synovial fluid examination
  • Essential if main differential diagnosis is between gout and septic joint – otherwise not used very often
  • Cell count – predominance of polymorphonuclear cells
    • Absolute WBC cell count usually <50,000
  • Crystals – presence of uric acid crystals in fluid as viewed by polarized light microscopy is diagnostic
  • Gram stain and culture to rule out septic arthritis
• Serum uric acid
  • Elevated in only 50% of patients during an acute attack
    • Lack of elevation does not rule out gout
  • Ideally measured >4 weeks after an acute attack
    • Repeat when joint normalizes if normal value found during an attack
  • Ideal method – uricase (ACR/EULAR, 2015)
• CBC – modest leukocytosis may be present
  • Significant leukocytosis suggests septic joint
• BUN and creatinine – to evaluate renal function
  • Drugs used to treat acute and chronic gout may affect renal function

Imaging Studies

•  Acute gout – not useful
• Chronic gout – may demonstrate tophi; erosive joint disease

Differential Diagnosis

• Calcium pyrophosphate dihydrate disease (pseudogout)
• Reactive arthritis (eg, Campylobacter jejuni)
• Septic arthritis
• Cellulitis
• Osteoarthritis
• Rheumatoid arthritis
• Internal ligament derangement
• Hemarthropathy
• Traumatic arthritis