Diagnosis: Gout
The most likely diagnosis is gout (Option A), despite the high-normal serum uric acid level. 1 This 30-year-old man presents with a classic pattern of recurrent monoarticular arthritis—two discrete, self-limited episodes affecting the same knee joint separated by several months—which strongly supports crystal arthropathy, specifically gout. 1
Why Gout Is Most Likely
Clinical Pattern Supports Crystal Arthropathy
- Recurrent, self-limited monoarticular episodes spaced months apart are the hallmark presentation of gout, even in younger adults when metabolic risk factors are present. 1
- The elevated serum urea suggests underlying renal impairment, which is a major risk factor for gout (relative risk 4.95) and warrants further evaluation. 1, 2
Critical Diagnostic Pitfall: Normal Uric Acid Does Not Exclude Gout
- EULAR guidelines explicitly caution that normal or high-normal serum uric acid levels should never be used to exclude gout when clinical features are suggestive. 1
- 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. 2
- The specificity of hyperuricemia for gout is only 53-61%, and its absence does not rule out the diagnosis. 1
Why Pseudogout Is Unlikely (Option B)
- Calcium pyrophosphate deposition disease (pseudogout) is exceedingly uncommon before age 60, making it highly unlikely in a 30-year-old patient. 1, 3
- Pseudogout typically affects larger joints following trauma, surgery, or ischemic events—none of which are present in this case. 3
Why Septic Arthritis Is Effectively Ruled Out (Option C)
- Septic arthritis does not resolve spontaneously without antibiotics and characteristically demands urgent antimicrobial therapy. 1
- This patient remains afebrile, hemodynamically stable, with normal WBC, and experienced complete spontaneous resolution of his prior episode—all features that effectively exclude septic arthritis. 1
- The absence of fever, swelling, effusion, or systemic manifestations further argues strongly against infection. 1
Essential Next Steps Before Treatment
Joint Aspiration Is Mandatory
- Arthrocentesis during the next acute flare is essential before initiating long-term urate-lowering therapy. 1
- Synovial fluid analysis is the diagnostic gold standard: identification of needle-shaped, negatively birefringent monosodium urate crystals under polarized light microscopy confirms gout with sensitivity 63-78% and specificity 93-100%. 4, 2
Critical Safety Measure
- Gram stain and bacterial culture must be performed on all aspirated fluid, even when crystals are identified, because gout and septic arthritis can coexist. 1, 2, 5
- A synovial total nucleated count >50,000 cells with >90% polymorphonuclear cells and serum CRP >10 mg/dL raises high suspicion for concurrent septic arthritis (odds ratio 7.7). 6
Risk Factor Assessment
The elevated urea warrants evaluation for:
- Chronic kidney disease (relative risk for gout: 4.95) 2
- Medication review for diuretics, low-dose aspirin, cyclosporine, or tacrolimus (relative risk: 1.72) 2
- Metabolic syndrome components: obesity (relative risk: 3.81), hypertension (relative risk: 3.93), diabetes 2
- Dietary factors: alcohol consumption, purine-rich foods (red meat, shellfish), high-fructose corn syrup 2
Clinical Algorithm for This Patient
- Await next acute flare and perform immediate arthrocentesis with crystal analysis, Gram stain, and culture 1, 2
- If crystals confirm gout, initiate acute anti-inflammatory therapy (NSAIDs, colchicine, or corticosteroids) 2
- Evaluate renal function (creatinine, eGFR) given elevated urea 2
- Screen for cardiovascular comorbidities (hypertension, ischemic heart disease, heart failure, diabetes, dyslipidemia) 2
- Consider urate-lowering therapy if ≥2 flares per year, targeting serum uric acid <6.0 mg/dL 2