Allergic bronchopulmonary mycosis - pathophysiology, histology, diagnosis, and treatment

Abstract

Allergic bronchopulmonary mycosis (ABPM) develops mainly in patients with asthma or cystic fibrosis via types I and III hypersensitivity reactions to filamentous fungi. Aspergillus spp., especially Aspergillus fumigatus, is the major causative fungus because of its small conidia, thermophilic hyphae, and ability to secrete serine proteases. The cardinal histological feature of ABPM is allergic (eosinophilic) mucin-harboring hyphae in the bronchi, for which the formation of extracellular DNA trap cell death (ETosis) of eosinophils induced by viable fungi is essential. Clinically, ABPM is characterized by peripheral blood eosinophilia, increased IgE levels in the serum, IgE and IgG antibodies specific for fungi, and characteristic radiographic findings; however, there are substantial differences in the clinical features of this disease between East and South Asian populations. Systemic corticosteroids and/or antifungal drugs effectively control acute diseases, but recurrences are quite common, and development of novel treatments are warranted to avoid adverse effects and emergence of drug-resistance due to prolonged treatment with corticosteroids and/or antifungal drugs.

Keywords: Allergy; Aspergillus fumigatus; Eosinophils; Fungus.

Fig. 1. Histology of allergic (eosinophilic) mucin in the bronchi. Mucus plugs packed in the bronchi of surgically-resected lungs from a patient with allergic bronchopulmonary mycosis demonstrate a fir tree-like structure (A: H&E, x5), which contain many eosinophils, Charcot-Leyden crystals, and fibrin exudates (B: H&E, x40). (C) Hyphae of fungi are sparsely found in mucus plugs (Grocott staining, x40).