Differential Diagnosis of Bronchial Asthma
The differential diagnosis of bronchial asthma must systematically exclude large airway obstructions, other chronic airway diseases, cardiac causes, and conditions mimicking asthma symptoms, with the most critical distinctions being COPD in adults, vocal cord dysfunction, and foreign body aspiration in appropriate clinical contexts. 1
Age-Specific Differential Diagnoses
In Adults
COPD represents the most important differential diagnosis in adults, particularly in patients with a smoking history of ≥10 pack-years, slowly progressive dyspnea on exertion, little symptom variability, and poor response to bronchodilators 1. The key distinguishing feature is that COPD shows persistent airflow limitation (FEV1/FVC <70% post-bronchodilator) without significant reversibility 1.
Cardiovascular causes:
- Congestive heart failure presenting with dyspnea and wheezing ("cardiac asthma") 1
- Pulmonary embolism causing acute breathlessness 1
Drug-induced cough:
- ACE inhibitor-related cough, which can mimic asthma symptoms 1
Mechanical airway obstruction:
- Benign and malignant tumors causing fixed airway obstruction 1
- Enlarged lymph nodes compressing airways 1
In Children (Ages 0-4 Years)
Diagnosis in young children is particularly challenging due to difficulty obtaining objective lung function measurements 1. Avoid mislabeling with terms like "wheezy bronchitis," "recurrent pneumonia," or "reactive airway disease" as these delay appropriate asthma treatment and miss the opportunity to prevent chronic airway inflammation and structural changes 1.
Large Airway Obstructions
These conditions require immediate consideration when symptoms are atypical or unresponsive to standard asthma therapy:
- Foreign body in trachea or bronchus 1
- Vocal cord dysfunction (VCD) 1
- Vascular rings or laryngeal webs 1
- Laryngotracheomalacia, tracheal stenosis, or bronchostenosis 1
Vocal Cord Dysfunction (VCD)
VCD is a critical mimic of asthma that requires specific diagnostic approaches 1. Key distinguishing features include:
- Asthma medications provide little to no symptom relief 1
- Variable flattening of the inspiratory flow loop on spirometry strongly suggests VCD 1
- Diagnosis confirmed by direct or indirect vocal cord visualization during an episode showing abnormal adduction 1
- VCD should be specifically considered in patients with difficult-to-treat, atypical asthma and in elite athletes with exercise-related breathlessness unresponsive to asthma medication 1
- VCD may coexist with asthma, complicating diagnosis 1
Other Respiratory Causes
Chronic airway diseases:
- Bronchiectasis with chronic productive cough 2
- Cystic fibrosis in younger patients 1
- Obliterative bronchiolitis 1, 2
- Diffuse panbronchiolitis 2
Aspiration-related:
- Aspiration from swallowing mechanism dysfunction 1
- Gastroesophageal reflux disease (GERD), which may coexist with asthma and complicate diagnosis 1
Eosinophilic conditions:
- Pulmonary infiltration with eosinophilia 1
- Allergic bronchopulmonary aspergillosis, which may coexist with asthma 1, 2
- Churg-Strauss syndrome 2
Cough Variant Asthma
Cough can be the principal or only manifestation of asthma, especially in young children 1. This represents a diagnostic challenge rather than a differential diagnosis:
- Monitoring of peak expiratory flow or bronchoprovocation testing may be helpful 1
- Diagnosis is confirmed by positive response to asthma medications 1
- Recurrent cough not due to asthma must be excluded 1
Diagnostic Approach to Differentiation
Spirometry is essential and mandatory because medical history and physical examination alone are unreliable for excluding other diagnoses 1. Spirometry should demonstrate obstruction and assess reversibility in patients ≥5 years of age 1.
Additional testing when diagnosis is uncertain:
Bronchoprovocation testing (methacholine, histamine, cold air, or exercise challenge) when asthma is suspected but spirometry is normal or near-normal 1. A negative test is more helpful to rule out asthma than a positive test is to confirm it, as airway hyperresponsiveness can occur in other conditions 1.
Chest x-ray to exclude other diagnoses, particularly pneumonia and structural abnormalities 1
Additional pulmonary function studies including diffusing capacity for COPD evaluation, lung volume measurements for restrictive defects, and evaluation of inspiratory flow-volume loops for VCD 1
Comorbid Conditions That Complicate Diagnosis
Three conditions frequently coexist with asthma and complicate the diagnostic picture:
- Gastroesophageal reflux disease (GERD) 1
- Obstructive sleep apnea (OSA) 1
- Allergic bronchopulmonary aspergillosis 1
When to Refer
Consider referral to an asthma specialist when: