Allergic Bronchopulmonary Aspergillosis (ABPA)

ABPA is a complex immunologic disorder in which Aspergillus fumigatus colonizes the airways and triggers IgE- and IgG-mediated hypersensitivity, eosinophilic inflammation, mucus impaction, and progressive airway remodeling. It occurs in 1-15% of patients with poorly controlled asthma and 2-15% of cystic fibrosis patients. Repeated allergic and inflammatory cascades produce central bronchiectasis with mucus plugging, atelectasis, and fixed airflow limitation.

Diagnostic criteria (Greenberger or ISHAM revised) require asthma or CF, immediate Aspergillus skin test or specific IgE positivity, total IgE >1000 IU/mL (or rising 4-fold during flare), elevated specific IgG to Aspergillus, eosinophilia >500 cells/μL, and chest imaging features such as central bronchiectasis, fleeting infiltrates, mucoid impactions, and high-attenuation mucus on CT. Sputum culture or PCR for Aspergillus may be supportive but is not definitive.

Five clinical stages guide management: stage I (acute), stage II (remission), stage III (exacerbation), stage IV (steroid-dependent asthma), and stage V (fibrotic). Oral prednisone 0.5 mg/kg/day for 2 weeks tapered over 6-8 weeks treats acute disease and exacerbations. Itraconazole 200 mg twice daily for 16 weeks reduces fungal burden and steroid requirement; voriconazole and posaconazole are alternatives. For severe steroid-dependent disease, biologic therapy with omalizumab (anti-IgE), mepolizumab or benralizumab (anti-IL-5/IL-5R), or dupilumab (anti-IL-4Rα) reduces exacerbations. Fibrotic stage requires symptomatic management and pulmonary rehabilitation.