How to differentiate bronchitis from asthma in adults with respiratory symptoms and potential allergies?

Differentiating Bronchitis from Asthma in Adults

In adults with respiratory symptoms, asthma is characterized by recurrent, variable episodes of wheeze and dyspnea that worsen at night or with triggers, while acute bronchitis presents as a single, self-limited episode of cough lasting less than 3 weeks without a history of similar episodes. 1

Critical Historical Features That Distinguish These Conditions

Pattern of Episodes:

• Asthma: Recurrent attacks with at least two similar doctor-diagnosed episodes in the past 5 years indicates a 65% probability of underlying asthma rather than repeated bronchitis 1
• Acute Bronchitis: Single, isolated episode of cough with or without sputum production, lasting no more than 3 weeks 2, 1
• If cough persists beyond 3 weeks, acute bronchitis is excluded and asthma must be considered 2, 1

Symptom Characteristics:

• Asthma: Symptoms are variable, intermittent, worse at night, and provoked by specific triggers including exercise, allergens, cold air, or aspirin 2
• Asthma: Progressively worsening shortness of breath, wheezing, and chest tightness are hallmark features 1
• Bronchitis: Symptoms are more constant throughout the day without the characteristic nocturnal worsening or trigger-based pattern 1
• Bronchitis: Cough is the predominant manifestation, not episodic dyspnea 3

Associated Features:

• Asthma: Personal or family history of atopy (eczema, allergic rhinitis), female sex, and history of allergy are predictive 2
• Asthma: Wheezing and prolonged expiration on examination are strong predictors 2, 3
• Bronchitis: Often follows a viral upper respiratory prodrome with no atopic background 2

Objective Testing: Essential for Accurate Diagnosis

Spirometry or peak flow measurement is mandatory because symptoms alone are unreliable for distinguishing these conditions. 2, 1

Spirometry Findings:

• Asthma: Demonstrates reversible airflow obstruction with ≥12% and ≥200 mL improvement in FEV₁, or ≥20% improvement in peak expiratory flow after bronchodilator 1
• Acute Bronchitis: May show transient airflow obstruction in 40% of patients, but this resolves within 6 weeks and does not show the characteristic reversibility pattern of asthma 4, 3
• Up to 17% of patients with presumed acute bronchitis show >15% FEV₁ reversibility, suggesting underlying reactive airway disease 3

When Baseline Spirometry is Normal:

• If FEV₁ is ≥70% predicted but clinical suspicion for asthma remains high, bronchial provocation testing with methacholine, histamine, cold air, or exercise challenge should be performed 2, 1
• A positive bronchoprovocation test is consistent with asthma; a negative test effectively rules it out 2

Physical Examination Findings

During Acute Episodes:

• Asthma: Diffuse, polyphonic, bilateral wheeze (particularly expiratory), prolonged expiration, hyperinflation, use of accessory muscles, hunched shoulders 2
• Asthma: May have signs of atopic dermatitis or eczema 2
• Bronchitis: May have adventitious sounds but without the characteristic prolonged expiration or hyperinflation 2

Between Episodes:

• Asthma: Physical examination may be completely normal, which does not exclude the diagnosis 2
• Bronchitis: By definition resolves completely within 3 weeks 2, 3

Critical Diagnostic Pitfalls to Avoid

The Most Common Misdiagnosis:

• Approximately one-third of patients presenting with acute cough are misdiagnosed as having acute bronchitis when they actually have asthma 4
• In retrospective studies, 65% of patients with recurrent "acute bronchitis" episodes actually had mild asthma 4
• Up to 45% of patients with acute cough lasting more than 2 weeks have asthma or COPD, not bronchitis 2, 3

Red Flags Indicating Asthma Rather Than Bronchitis:

• Two or more similar episodes in the past 5 years 1
• Cough persisting beyond 3 weeks 2, 1, 4
• Presence of wheezing, prolonged expiration, smoking history, and symptoms of allergy (having at least two of these features warrants lung function testing) 2
• Nocturnal symptoms or trigger-based symptom patterns 2, 1

Additional Testing Considerations

Tests NOT Routinely Indicated for Acute Bronchitis:

• Chest x-ray, sputum culture, viral PCR, C-reactive protein, or procalcitonin have no added predictive value over history and physical examination for ruling out pneumonia or confirming acute bronchitis 2
• These tests should only be obtained if pneumonia is suspected based on vital sign abnormalities (heart rate >100 beats/min, respiratory rate ≥24-30 breaths/min, temperature >37.8-38°C) or focal chest examination findings 2, 3

Tests That May Support Asthma Diagnosis:

• Peripheral blood or sputum eosinophilia supports asthma diagnosis when other causes of eosinophilia are excluded 5
• Elevated serum IgE supports asthma diagnosis, though normal levels do not exclude it 5
• Positive skin tests establish atopic state 5

Management Implications of Correct Diagnosis

For Confirmed Acute Bronchitis:

• Antibiotics are NOT indicated and should not be offered, as viruses cause >90% of cases 2, 1, 3
• Only symptomatic treatment with antitussive agents for short-term relief 2
• Expected resolution within 3 weeks 2, 3

For Confirmed Asthma:

• Beta-agonists and inhaled corticosteroids are beneficial and form the basis of treatment 3, 6
• For acute exacerbations with inadequate response to bronchodilators, oral corticosteroids (prednisone 40-60 mg daily for 5-7 days) are recommended 1
• Long-term controller therapy with inhaled corticosteroids is essential 6

High-Risk Asthma Patients Requiring Intensive Monitoring:

• Previous severe exacerbation requiring intubation or ICU admission 1
• Two or more hospitalizations or three or more ED visits for asthma in the past year 1
• Using more than 2 canisters of short-acting beta-agonist per month 1