Bronchial Asthma

Bronchial Asthma

1. Definition & disease concept

• Bronchial asthma is a chronic inflammatory disorder of the airways characterised by hyper-responsiveness of tracheobronchial smooth muscle to a wide variety of stimuli, producing recurrent, variable and reversible airflow obstruction with wheeze, dyspnoea, chest tightness and cough (often nocturnal) (KDT 8e Ch.16, pp.241; R&D 10e Ch.28, pp.—).
• The three defining features are: chronic airway inflammation, bronchial hyper-reactivity, and variable/reversible airflow limitation — asthma is now framed as a heterogeneous disease rather than a single entity (R&D 10e Ch.28; Katzung 16e Ch.20, pp.363–4).
• Asthma is dually an obstructive disease (reversible bronchoconstriction) and an inflammatory disease (airway oedema, goblet-cell hyperplasia, mucus secretion, inflammatory-cell infiltration with cytokine release) — treatment must address both components: bronchodilators (relievers) and anti-inflammatory agents (controllers) (Golan 4e Ch.48, pp.877).
• The historical and clinically pivotal reframing: asthma is primarily an inflammatory condition in which inflammation underlies the hyper-reactivity; uncontrolled inflammation accentuates the disease over time and drives airway remodeling (KDT 8e Ch.16, pp.241; G&G 14e Ch.44, pp.875–6).
• Chronic inflammation in allergic asthma, although initially allergen-driven, becomes autonomous, so that asthma is essentially incurable — corticosteroids suppress inflammation but do not cure it; inflammation and symptoms return when steroids are stopped (G&G 14e Ch.44, pp.876, 887).
• Hallmark pathophysiology = widespread reversible narrowing of bronchial airways + markedly increased bronchial responsiveness to inhaled stimuli; pathology = lymphocytic, eosinophilic inflammation of the bronchial mucosa (Katzung 16e Ch.20, pp.363).

Severity & natural history

• Asthma severity is classified across two domains — impairment (frequency/severity of symptoms, degree of airflow obstruction, therapy intensity needed for control) and risk (susceptibility to exacerbations) (Katzung 16e Ch.20, pp.364).
• Impairment-based categories: mild intermittent, mild persistent, moderate persistent, severe persistent — but a patient is up-classified if history shows frequent/severe exacerbations ("exacerbation-prone" vs "exacerbation-resistant") (Katzung 16e Ch.20, pp.364).
• Risk factors for exacerbations: ≥1 exacerbation in the previous year, low lung function, poor adherence or incorrect inhaler technique, smoking, sputum or blood eosinophilia (Katzung 16e Ch.20, pp.364).
• Asthma severity usually does not progress — mild asthma rarely becomes severe; severe asthma is usually severe from onset. Exception: some late-onset patients show progressive loss of lung function resembling COPD (G&G 14e Ch.44, pp.876).
• Two classical clinical varieties (KDT framing): Extrinsic asthma — mostly episodic, allergic basis, less prone to status asthmaticus; Intrinsic asthma — perennial, status asthmaticus more common (KDT 8e Ch.16, pp.241).