What is the most likely diagnosis for a patient with sore throat and a productive cough with yellow sputum, no fever, no improvement after antibiotics, but rapid response to an inhaled corticosteroid?

Diagnosis: Cough-Variant Asthma or Non-Asthmatic Eosinophilic Bronchitis

The most likely diagnosis is cough-variant asthma (CVA) or non-asthmatic eosinophilic bronchitis (NAEB), given the failure to respond to antibiotics and rapid improvement with inhaled corticosteroids. 1

Clinical Reasoning

Why Antibiotics Failed

• Respiratory viruses cause 89-95% of acute bronchitis cases, making antibiotics ineffective regardless of sputum color or appearance 2, 3
• Yellow or green sputum occurs in 89-95% of viral bronchitis and does not indicate bacterial infection—it reflects inflammatory cells, not bacteria 2, 3
• The lack of fever strongly argues against bacterial infection, which typically presents with temperature >38°C persisting beyond 3 days 2

Why Inhaled Corticosteroids Worked

• Cough-variant asthma responds specifically to inhaled corticosteroids, with partial improvement often seen after 1 week but complete resolution requiring up to 8 weeks of treatment 1
• Non-asthmatic eosinophilic bronchitis also responds well to inhaled corticosteroids, as the underlying pathology is eosinophilic airway inflammation similar to asthma but without airway hyperresponsiveness 1
• The rapid response to steroid inhalers is pathognomonic for eosinophilic airway inflammation, not infectious bronchitis 1, 4

Distinguishing Between CVA and NAEB

Cough-Variant Asthma

• Characterized by cough as the sole or predominant symptom of asthma 1
• May have airway hyperresponsiveness on methacholine challenge testing 1
• Approximately 30% progress to classical asthma with wheezing over 4 years 4
• Responds to standard asthma therapy: inhaled bronchodilators plus inhaled corticosteroids 1

Non-Asthmatic Eosinophilic Bronchitis

• Presents with chronic cough and sputum eosinophilia but no airway hyperresponsiveness or variable airflow obstruction 1
• Accounts for 10-30% of chronic cough cases in specialist referral populations 1
• Responds to inhaled corticosteroids alone without requiring bronchodilators 1
• Diagnosis confirmed by sputum eosinophilia (>3% eosinophils on induced sputum) 1

Recommended Diagnostic Workup

• Perform spirometry with bronchodilator response testing to differentiate asthma (≥12% and ≥200 mL FEV₁ improvement) from NAEB (normal spirometry and no bronchodilator response) 4
• Consider induced sputum analysis if available to document eosinophilic inflammation (>3% eosinophils confirms eosinophilic bronchitis) 1
• Measure fractional exhaled nitric oxide (FeNO) as a non-invasive marker of eosinophilic inflammation and predictor of corticosteroid responsiveness 1, 4
• Methacholine challenge testing can help distinguish CVA (positive test) from NAEB (negative test) 1

Treatment Approach

First-Line Therapy

• Continue inhaled corticosteroids as first-choice treatment for both CVA and NAEB (Grade 1B for asthma, Grade 2B for NAEB) 1
• For CVA, combine with inhaled β₂-agonists as standard asthma therapy 1
• For NAEB, inhaled corticosteroids alone are typically sufficient 1

If Response Is Incomplete

• Step up the inhaled corticosteroid dose and consider adding a leukotriene receptor antagonist after reconsidering alternative causes of cough 1
• For severe or refractory cases, a short course of oral prednisone (40 mg daily for 1 week) may be necessary 1
• Complete resolution may require up to 8 weeks of treatment 1

Common Pitfalls to Avoid

• Do not assume bacterial infection based on purulent sputum alone—this occurs in 89-95% of viral cases 2, 3
• Do not prescribe antibiotics for persistent cough without fever—approximately one-third of patients diagnosed with "recurrent acute bronchitis" actually have undiagnosed asthma 2
• Do not stop inhaled corticosteroids prematurely—complete cough resolution may take up to 8 weeks 1
• Watch for inhaled steroid-induced cough from the aerosol dispersant itself, which may require switching formulations 1
• Rule out gastroesophageal reflux disease (GERD) as a co-factor making asthma difficult to control 1

When to Reassess

• If cough persists beyond 3 weeks despite appropriate inhaled corticosteroid therapy, consider alternative diagnoses including GERD, upper airway cough syndrome, or pertussis 2
• If fever develops or persists >3 days, reassess for bacterial superinfection or pneumonia 2
• If symptoms worsen rather than gradually improve, reevaluate the diagnosis 2