What is the next appropriate step in management for a 9-year-old boy with a recent respiratory tract infection, left knee swelling with limited range of motion, right ankle pain, and a systolic ejection murmur?

Acute Rheumatic Fever: Initiate Acetylsalicylic Acid Immediately

This 9-year-old boy presents with classic acute rheumatic fever (ARF) following a streptococcal upper respiratory infection, manifesting as migratory polyarthritis (left knee, right ankle) and carditis (systolic ejection murmur), and should be started on acetylsalicylic acid (aspirin) as first-line anti-inflammatory therapy.

Clinical Reasoning

This presentation fulfills the Jones Criteria for acute rheumatic fever:

• Major criteria: Polyarthritis (migratory joint involvement) + carditis (new murmur)
• Temporal relationship: 3 weeks post-upper respiratory infection (typical latency period for post-streptococcal sequelae)
• Age and demographics: 9 years old (peak incidence 5-15 years)

The combination of migratory arthritis affecting large joints with limited range of motion, no effusion, and a new cardiac murmur in the context of recent pharyngitis is pathognomonic for ARF rather than other post-infectious arthritides.

Why Acetylsalicylic Acid (Option B) is Correct

Aspirin remains the cornerstone anti-inflammatory treatment for acute rheumatic fever with arthritis. 1

• Dosing: 80-100 mg/kg/day divided into 4-6 doses (maximum 6-8 g/day) for arthritis control
• Duration: Continue until inflammatory markers normalize and symptoms resolve (typically 4-6 weeks), then taper gradually
• Mechanism: Provides both anti-inflammatory and analgesic effects for the severe joint inflammation characteristic of ARF 1

Important safety consideration: While aspirin carries a theoretical risk of Reye's syndrome in children with viral infections, this risk does not apply to ARF treatment, where aspirin is specifically indicated and has decades of safe use. 2 The FDA warning about Reye's syndrome pertains to viral illnesses (influenza, varicella), not post-streptococcal inflammatory conditions.

Why NOT Corticosteroids (Option A)

Corticosteroids are reserved for severe carditis with heart failure, not for uncomplicated arthritis. 3

• This patient has a murmur suggesting mild carditis but no signs of heart failure (no mention of dyspnea, edema, hepatomegaly, or cardiomegaly)
• Corticosteroids do not prevent long-term cardiac sequelae and carry significant adverse effects in children (growth suppression, immunosuppression, metabolic effects) 3
• The arthritis of ARF responds dramatically to aspirin alone, often within 24-48 hours, making corticosteroids unnecessary 1

Essential Concurrent Management

Beyond anti-inflammatory therapy, this patient requires:

Antibiotic Therapy

• Penicillin (benzathine penicillin G 1.2 million units IM × 1 dose, or oral penicillin V 250 mg TID × 10 days) to eradicate residual streptococcal infection
• Initiate secondary prophylaxis with monthly benzathine penicillin G injections to prevent recurrent ARF (duration: minimum 5 years or until age 21, whichever is longer; lifelong if carditis present)

Cardiac Evaluation

• Echocardiography to assess for valvular involvement (mitral regurgitation most common), ventricular function, and pericardial effusion
• ECG to evaluate for PR prolongation (first-degree AV block occurs in 30-40% of ARF cases)
• Serial cardiac assessments to monitor for progression of carditis

Laboratory Confirmation

• Anti-streptolysin O (ASO) titer or anti-DNase B to document recent streptococcal infection
• Acute phase reactants (ESR, CRP) to establish baseline and monitor treatment response
• Throat culture (though often negative by 3 weeks post-infection)

Monitoring and Follow-Up

• Clinical response: Arthritis should improve dramatically within 24-48 hours of aspirin initiation; lack of response should prompt reconsideration of the diagnosis
• Salicylate levels: Target 20-25 mg/dL for therapeutic effect; monitor for toxicity (tinnitus, hyperventilation, altered mental status)
• Inflammatory markers: ESR/CRP should normalize over 4-6 weeks; persistent elevation may indicate ongoing inflammation or treatment failure
• Cardiac surveillance: Repeat echocardiography at 2 weeks, 6 weeks, and 6 months to detect evolving valvular disease

Common Pitfalls to Avoid

• Do not delay aspirin while awaiting laboratory confirmation; ARF is a clinical diagnosis and treatment should begin immediately to prevent cardiac complications
• Do not use NSAIDs other than aspirin (e.g., ibuprofen, naproxen); aspirin has the most extensive evidence base in ARF and allows therapeutic drug monitoring 1, 4
• Do not stop aspirin abruptly; taper gradually over 1-2 weeks to prevent rebound inflammation
• Do not forget secondary prophylaxis; recurrent ARF episodes cause cumulative cardiac damage and significantly worsen prognosis