What is the diagnosis and treatment for a patient with migratory joint pains and a positive Antistreptolysin O (ASO) titer?

Diagnosis: Acute Rheumatic Fever (ARF) or Post-Streptococcal Reactive Arthritis (PSRA)

A patient presenting with migratory joint pains and positive ASO titer most likely has acute rheumatic fever (ARF) and requires immediate antibiotic therapy with penicillin V 500 mg orally twice or three times daily for 10 days to eradicate streptococcal infection and prevent permanent cardiac valve damage. 1

Diagnostic Approach

Confirm the Diagnosis Using Jones Criteria

The positive ASO titer confirms preceding streptococcal infection, which is essential for diagnosing post-streptococcal complications. 1 You must now determine if this is ARF or PSRA:

Acute Rheumatic Fever (ARF) features:

• Migratory polyarthritis affecting large joints (knees, ankles, wrists, elbows) that responds dramatically to salicylates/NSAIDs 2
• Arthritis typically resolves in each joint within days as it migrates to another joint 3
• May have additional major criteria: carditis, chorea, erythema marginatum, subcutaneous nodules 1
• Arthritis improves rapidly with anti-inflammatory therapy 4

Post-Streptococcal Reactive Arthritis (PSRA) features:

• Cumulative and persistent arthritis (does not migrate and resolve) 4
• Can involve large joints, small joints, or axial skeleton 4
• Does NOT respond well to salicylates 4
• Occurs approximately 10 days after group A streptococcal pharyngitis 4

Additional Diagnostic Testing Required

Cardiac evaluation is mandatory:

• Perform ECG and echocardiogram to assess for carditis, as both ARF and PSRA can progress to valvular heart disease 1, 4
• The American Heart Association recommends monitoring for cardiac involvement in all post-streptococcal cases 4

Laboratory confirmation:

• If ASO is not significantly elevated, add anti-DNase B testing (combined testing detects up to 98% of cases) 1, 5
• Anti-DNase B peaks later (6-8 weeks) than ASO (3-6 weeks), providing complementary diagnostic information 1, 5
• Inflammatory markers (ESR, CRP) should be elevated 6

Exclude alternative diagnoses:

• Rule out septic arthritis with joint aspiration if a single joint is severely affected 2
• Consider crystal arthropathies (gout, pseudogout) with synovial fluid analysis 4
• Adult-onset Still's disease presents with quotidian fever >39°C, salmon-pink rash, and extremely elevated ferritin 6

Treatment Protocol

Immediate Antibiotic Therapy (Mandatory)

First-line treatment:

• Penicillin V 500 mg orally twice or three times daily for 10 days, OR 1
• Amoxicillin 50 mg/kg orally once daily for 10 days 1

Penicillin-allergic patients:

• Cephalosporins, clindamycin, or azithromycin (consider local resistance patterns) 1

Critical point: The 10-day duration is non-negotiable; shorter courses increase the risk of ARF and do not prevent cardiac complications. 1

Anti-Inflammatory Therapy

For ARF with arthritis:

• Naproxen or other NSAIDs provide rapid symptom relief (typically within 24-48 hours) 7
• If NSAIDs alone are insufficient, add corticosteroids 6

For PSRA with persistent arthritis:

• NSAIDs are first-line but often inadequate 4
• Consider sulfasalazine as a disease-modifying antirheumatic drug (DMARD) for persistent symptoms 4
• Corticosteroids may be required for severe cases 6

Secondary Prophylaxis (Essential for ARF)

Duration depends on cardiac involvement:

• Without carditis: Continuous oral penicillin prophylaxis for 5 years OR until age 21 (whichever is longer) 1
• With carditis but no residual valve disease: 10 years OR until age 21 (whichever is longer) 1
• With residual valve disease: Lifelong prophylaxis may be required 1

Follow-Up Monitoring

Short-term surveillance:

• Repeat clinical assessment at 3-5 days after initiating therapy 1
• Weekly follow-up until asymptomatic 1
• Monitor for development of carditis or glomerulonephritis 1

Cardiac monitoring:

• Serial echocardiograms to detect valvular damage, particularly in PSRA which may occasionally progress to valvular heart disease 4

Common Pitfalls to Avoid

Do not confuse chronic carriage with active infection:

• Up to 20% of asymptomatic school-age children are GAS carriers during winter/spring 8
• An elevated ASO alone does not distinguish active infection from recent past infection, as titers remain elevated for months 1, 8

Do not delay antibiotic therapy:

• The primary objective is preventing permanent cardiac valve damage and mortality 1
• Even if ARF is suspected rather than confirmed, treat immediately while completing diagnostic workup 1

Do not assume all migratory arthritis is ARF:

• Adult-onset Still's disease can present with migratory arthralgia but has distinctive quotidian fever pattern, evanescent rash, and extremely elevated ferritin 6
• Reactive arthritis from other triggers (GI/GU infections) may present similarly but lacks elevated streptococcal antibodies 4