Definition
• A chronic inflammatory disorder of the airways in which many cells and cellular elements play a role. In susceptible individuals, this inflammation causes recurrent episodes of wheezing, breathlessness, chest tightness, and coughing, particularly at night and in the early morning. These episodes are usually associated with widespread but variable airflow obstruction that is often reversible either spontaneously or with treatment.
Clinical features
Epidemiology
• A major health problem affecting more than 15 million people in the United States
• The incidence and prevalence has increased in the last 3 to 4 decades
Presentation
• Recurrent episodes of shortness of breath, wheezing, coughing, and chest tightness
• These symptoms are associated with airflow obstruction, which is reversible either spontaneously or with treatment
• Spirometry measurement shows significant reversibility of airflow obstruction
Prognosis and treatment
• Children with mild disease have a good prognosis. Approximately half of patients will no longer have the diagnosis after a decade
• Quick-relief medications used to treat acute symptoms (e.g. short-acting β2-adrenoceptor agonists) and long-term control medications used to prevent further exacerbation (e.g., inhaled glucocorticoids)
Pathology
Histology
• Gross autopsy findings of patients with status asthmaticus: mucous plugs occluding primarily medium-sized and small bronchi, associated with overinflation of the lungs
• Small bronchi are usually most severely affected and filled with mucous plugs. The mucus is mixed with eosinophils, shedding epithelium and Charcot-Leyden crystals
• Bronchial epithelium often desquamated but basal layer remains
• Prominent basal membrane thickening, goblet cell hyperplasia, and smooth muscle hyperplasia
• Squamous metaplasia may be seen
• The airways are infiltrated with eosinophils and mixed inflammatory cells
• Chronic asthma
• Constrictive bronchiolitis with submucosal scarring, concentric luminal narrowing, adventitial scarring, and chronic inflammation
• Bronchiectasis: walls of the cartilaginous bronchi are permanently destroyed, which results in permanent dilation of the airways and accompanied inflammatory changes
Immunopathology/special stains
• Not contributory
Main differential diagnoses
• Chronic bronchitis: clinically defined as a productive cough of unknown cause, occurring on most days for 3 or more months for at least 2 successive years; often associated with history of smoking; histologically characterized by chronic inflammation with basement membrane thickening, bronchial epithelial hyperplasia, and goblet cell metaplasia
• Eosinophilic pneumonia: clinical presentation is different from asthma. Patients usually do not have recurrent episodes of wheezing, shortness of breath, and coughing. Also they do not respond well to bronchial dilators. Eosinophilic pneumonia can be idiopathic or secondary to infections, drug administration, or associated with immunologic diseases. Clinical history and accessory tests (e.g., pulmonary function test) are helpful for differential diagnosis
Fig 1 Asthma. Endobronchial biopsy shows asthmatic changes including epithelial sloughing, basement membrane thickening, and marked eosinophilic inflammation.
Fig 2 Asthma. A, Bronchiole is severely affected. It has epithelial hyperplasia, prominent goblet cell metaplasia, basement membrane thickening, smooth muscle hyperplasia, and inflammatory cell infiltration with predominant eosinophils. B and C, Same patient with bronchial involvement. Histological findings are similar to that in the bronchiole.
Fig 3 Asthma. Squamous metaplasia of the bronchiolar epithelium is seen in this treated asthmatic patient without inflammation.
Fig 4 Asthma. Hyperplastic bronchial mucous glands are seen in this patient with history of asthma.