What is asthmatic bronchitis?

What is Asthmatic Bronchitis?

Asthmatic bronchitis is a condition characterized by features of both asthma and bronchitis, presenting with chronic cough, airway inflammation, and variable airflow limitation that may not fully meet the criteria for classic asthma.

Definition and Pathophysiology

Asthmatic bronchitis represents an overlap condition that includes elements of:

1. Airway inflammation - Similar to asthma, there is underlying inflammation in the airways 1
2. Bronchial hyperresponsiveness - Increased sensitivity of airways to various triggers 2
3. Chronic mucus hypersecretion - A feature more commonly associated with bronchitis 2

The condition typically presents in two main forms:

• Non-asthmatic eosinophilic bronchitis (NAEB) - Characterized by:

  • Corticosteroid-responsive chronic cough
  • Sputum eosinophilia (≥3% non-squamous cells)
  • Absence of variable airflow obstruction
  • Normal airway hyperresponsiveness (negative methacholine challenge) 1

• Cough-variant asthma - A form of asthma where cough is the predominant or only symptom, with:

  • Positive airway hyperresponsiveness
  • Response to bronchodilators
  • May progress to classic asthma in some cases 1

Clinical Features

The main clinical manifestations include:

• Chronic cough (lasting ≥8 weeks)
• May have wheezing, shortness of breath, and chest tightness
• Often worse at night or early morning
• May be triggered by allergens, irritants, exercise, or respiratory infections 1

Diagnostic Approach

Diagnosis requires:

1. Clinical assessment - Evaluation of symptoms and triggers
2. Pulmonary function testing - To assess for variable airflow limitation
3. Bronchial challenge testing - To evaluate airway hyperresponsiveness
4. Assessment of airway inflammation - Through induced sputum analysis, blood eosinophil count, or FeNO measurement 1

The key diagnostic distinction between NAEB and asthma is:

• NAEB: Normal airway hyperresponsiveness, no variable airflow obstruction
• Asthma: Positive airway hyperresponsiveness, variable airflow obstruction 1

Treatment

Treatment approaches differ based on the specific diagnosis:

For Non-asthmatic Eosinophilic Bronchitis:

• First-line: Inhaled corticosteroids (ICS) 1
• If response is incomplete:
  • Increase ICS dose
  • Consider adding leukotriene receptor antagonists 1

For Cough-variant Asthma or Asthmatic Features:

• Follow step-wise asthma treatment protocols:
  • Short-acting beta-agonists (SABA) for symptom relief
  • ICS as controller medication
  • Add-on therapies as needed (long-acting beta-agonists, leukotriene modifiers) 1

Natural History and Prognosis

The long-term outcomes vary:

• NAEB:

  • May be self-limiting in some cases
  • Can persist in approximately 66% of patients
  • Progression to classic asthma occurs in about 9% of cases
  • Fixed airflow obstruction develops in approximately 16% of patients 1

• Cough-variant asthma:

  • May progress to classic asthma in approximately 30% of cases 1

Common Pitfalls in Management

1. Misdiagnosis - Failing to distinguish between NAEB and asthma due to not performing appropriate tests for airway inflammation and hyperresponsiveness 1

2. Inadequate treatment - Insufficient dose or duration of ICS therapy, particularly in NAEB 1

3. Overlooking comorbidities - Not addressing concurrent conditions like GERD or upper airway cough syndrome that may contribute to persistent cough 1

4. Smoking - Not addressing smoking status, which can reduce response to corticosteroids and complicate management 1

5. Lack of follow-up - Not monitoring for progression to classic asthma or development of fixed airflow obstruction 1

By understanding the distinct features of asthmatic bronchitis and its variants, clinicians can provide appropriate targeted therapy to improve symptoms, quality of life, and prevent potential long-term airway remodeling.