Allergic Bronchopulmonary Aspergillosis

Allergic bronchopulmonary aspergillosis (ABPA) is an immune-mediated hypersensitivity reaction to Aspergillus species colonizing the airways, most commonly affecting patients with asthma or cystic fibrosis. Emerging evidence indicates that ABPA also occurs in individuals with COPD, post-tuberculosis lung disease, and non–cystic fibrosis bronchiectasis; however, asthma and cystic fibrosis remain the primary risk populations. The Infectious Diseases Society of America (IDSA) classifies ABPA as an allergic syndrome rather than an invasive fungal infection. In susceptible individuals, airway colonization by Aspergillus fumigatus triggers an exaggerated immune response characterized by elevated total immunoglobulin E (IgE), Aspergillus-specific IgE and IgG antibodies, and eosinophilia. The resulting inflammatory reaction produces the clinical manifestations of ABPA. ABPA commonly presents as poorly controlled asthma, mucoid impaction (sometimes mistaken for pneumonia), persistent eosinophilia, bronchiectasis, and immunologic evidence of allergy to Aspergillus antigens. In patients with cystic fibrosis, it typically manifests as difficult-to-control exacerbations that respond to corticosteroids. If untreated, ABPA may progress to bronchiectasis, pulmonary fibrosis, and irreversible lung damage. Rarely, fungi other than Aspergillus can produce a similar syndrome, allergic bronchopulmonary mycosis (ABPM), and some patients with severe asthma exhibit fungal sensitization without meeting full diagnostic criteria, a condition termed severe asthma with fungal sensitization. Treatment strategies target both suppression of the immune response and reduction of fungal burden to decrease antigenic stimulation.