What is the difference between bronchiolitis and asthma?

Differences Between Bronchiolitis and Asthma

Bronchiolitis is an acute viral lower respiratory tract infection primarily affecting infants under 2 years of age, while asthma is a chronic inflammatory disorder characterized by recurrent episodes of airflow obstruction, bronchial hyperresponsiveness, and underlying inflammation that can affect individuals of any age. 1

Key Differences

Definition and Pathophysiology

Bronchiolitis:

• Acute viral infection of the lower respiratory tract affecting small airways (bronchioles)
• Characterized by inflammation, edema, and necrosis of epithelial cells lining small airways
• Increased mucus production causing airway obstruction
• Primarily affects infants under 2 years of age
• Self-limiting condition in most children 1

Asthma:

• Chronic inflammatory disorder of the airways
• Involves multiple cell types (mast cells, eosinophils, T lymphocytes, macrophages)
• Characterized by variable and recurring symptoms
• Features bronchial hyperresponsiveness and airflow obstruction
• Can affect individuals of any age
• Often involves airway remodeling with persistent structural changes 1

Etiology

Bronchiolitis:

• Primarily caused by viral infections:
  • Respiratory syncytial virus (RSV) - most common
  • Human rhinovirus
  • Human metapneumovirus
  • Influenza
  • Adenovirus
  • Coronavirus
  • Parainfluenza viruses 1

Asthma:

• Multifactorial etiology involving genetic and environmental factors
• Triggered by various stimuli:
  • Allergens
  • Respiratory infections
  • Exercise
  • Cold air
  • Air pollutants
  • Strong emotions 1

Clinical Presentation

Bronchiolitis:

• Typically begins with rhinitis and cough
• May progress to tachypnea, wheezing, rales
• Use of accessory muscles and/or nasal flaring
• Highest incidence between December and March in North America
• Primarily affects children aged 1-23 months 1

Asthma:

• Recurrent episodes of wheezing, breathlessness, chest tightness, and coughing
• Symptoms often worse at night or early morning
• Variable airflow limitation that is often reversible
• Symptoms triggered by specific exposures
• Can affect any age group 1

Diagnostic Approach

Bronchiolitis:

• Clinical diagnosis based on history and physical examination
• Chest radiographs not routinely indicated
• Viral testing not necessary for typical presentations
• Laboratory evaluation not recommended for routine cases 2

Asthma:

• History of recurrent respiratory symptoms
• Evidence of variable airflow limitation (spirometry)
• Documentation of reversibility with bronchodilators
• Assessment of allergic status
• Exclusion of alternative diagnoses 1

Management

Bronchiolitis:

• Primarily supportive care:
  • Adequate hydration
  • Nasal suctioning to clear secretions
  • Supplemental oxygen if SpO₂ <90%
• Medications generally not recommended:
  • Bronchodilators not routinely recommended
  • Corticosteroids not recommended
  • Antibiotics only for specific bacterial co-infection 1, 2

Asthma:

• Pharmacologic therapy:
  • Bronchodilators for symptom relief
  • Inhaled corticosteroids for long-term control
  • Leukotriene modifiers
  • Biologic agents for severe asthma
• Environmental control measures
• Patient education and self-management 1

Relationship Between Bronchiolitis and Asthma

• Infants hospitalized with bronchiolitis are at increased risk for developing recurrent wheezing and childhood asthma 3, 4
• The causality direction remains uncertain - bronchiolitis may either contribute to asthma development or simply identify infants predisposed to asthma 3, 5
• Both host factors (prematurity, atopic predisposition) and viral infection characteristics (type of virus, severity) appear to play roles in this relationship 3, 4
• Recent research has identified distinct endotypes of bronchiolitis with differential risks of developing asthma 4

Clinical Implications

• Diagnosis patterns vary significantly with age - bronchiolitis predominates in infants <3 months (98% of encounters), while asthma diagnoses increase with age (44% of encounters at 23 months) 6
• For children with chronic cough after acute viral bronchiolitis, asthma medications should not be used unless other evidence of asthma is present 1
• The American Academy of Pediatrics recommends against routine use of bronchodilators in bronchiolitis, except in select cases with audible wheezing and objective evaluation of response 2
• Parents often ask about the risk of asthma development following bronchiolitis - clinicians should acknowledge the association while explaining that not all children with bronchiolitis will develop asthma 3

Common Pitfalls to Avoid

1. Misdiagnosing asthma as bronchiolitis in older infants (12-23 months) or vice versa
2. Inappropriately treating bronchiolitis with asthma medications
3. Failing to recognize that diagnostic patterns vary widely between hospitals and providers 6
4. Not considering host factors and viral characteristics when assessing risk for subsequent asthma
5. Overusing diagnostic tests (chest radiographs, viral testing) in typical cases of bronchiolitis

By understanding these key differences, clinicians can more accurately diagnose and appropriately manage these distinct but related respiratory conditions.