Obstructive lung diseases — bronchial asthma and bronchiectasis

A) Chronic Bronchitis

Definition

• Long-term inflammation of the bronchi
• Clinical diagnosis: persistent productive cough with sputum for 3 consecutive months in at least 2 consecutive years
• Common in cigarette smokers and urban residents (air pollution)

Forms

1. Simple chronic bronchitis: productive cough with mucoid sputum; no airflow obstruction
2. Chronic asthmatic bronchitis: hyperresponsive airways; intermittent bronchial spasms and wheezing
3. Chronic obstructive bronchitis: chronic outflow obstruction; usually associated with emphysema; common in heavy smokers

Pathogenesis

• Mucus hypersecretion is the hallmark:
  • Environmental toxins (smoking + pollution) → hypertrophy of mucous glands in trachea and bronchi → ↑ goblet cells in smaller bronchi/bronchioles
• Airway obstruction from:
  • Small airway disease: goblet cell metaplasia → mucus plugging + bronchiolar wall inflammation and fibrosis
  • Coexistent emphysema

Morphology

Macroscopy:

• Mucosal lining is hyperemic and swollen by edema fluid
• Often covered by mucopurulent secretions

Microscopy:

• Enlargement of mucus-secreting glands (trachea and bronchi)
• Reid index: ratio of gland layer thickness to bronchial wall thickness (epithelium to cartilage)
  • Normally 0.4; increased in chronic bronchitis
• Inflammatory cell infiltration of bronchial mucosa
• Chronic bronchiolitis: goblet cell metaplasia, mucus plugging, inflammation, fibrosis
• Bronchiolitis obliterans: lumen completely obliterated by fibrosis

Clinical features

• Prominent cough with sputum production, initially without airflow obstruction
• Some progress to COPD with airflow obstruction + hypercapnia + hypoxemia + cyanosis → “blue bloaters”
• Progression: pulmonary hypertension + cardiac failure

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B) Bronchiectasis

Definition

• Permanent dilation of the bronchial wall caused by destruction of muscle and elastic tissue, associated with chronic necrotizing infections

Predisposing conditions

1. Bronchial obstruction: tumor, foreign body, mucus plugs (limited to obstructed segment)
2. Congenital/hereditary:
   • Cystic fibrosis: widespread bronchiectasis from mucus plugs
   • Immunodeficiency: repeated bacterial infections
   • Kartagener syndrome (primary ciliary dyskinesia): structural cilia abnormalities → impaired mucociliary clearance → bronchiectasis
3. Necrotizing/suppurative pneumonia: virulent organisms (S. aureus, Klebsiella)

Pathogenesis

Two key processes: obstruction + chronic persistent infection

• Obstruction → impaired clearance → secondary infection → inflammatory wall damage + exudate accumulation → irreversible dilation
• Persistent necrotizing inflammation → obstructive secretions + wall destruction → dilation

Morphology

Macroscopy: Markedly distended peripheral bronchi (lower lobes), traceable to pleural surface

Microscopy:

• Intense acute and chronic inflammatory exudate in bronchial/bronchiolar walls
• Desquamation of lining epithelium → ulceration
• Healing → usually ends in dilation and scarring (not full regeneration)

Clinical features

• Cough, fever, purulent sputum (may contain blood)
• Clubbing of fingers
• Severe cases: hypoxemia, hypercapnia, pulmonary hypertension, cor pulmonale

💡 High-yield: Chronic bronchitis = clinical diagnosis (productive cough ≥3 months/yr for ≥2 yr); Reid index ↑; mucus gland hypertrophy; “blue bloater”. Bronchiectasis = permanent bronchial dilation; causes: CF, Kartagener (ciliary dyskinesia), immunodeficiency, necrotizing pneumonia; symptoms: cough + purulent sputum + fever + finger clubbing.