Allergic Bronchopulmonary Aspergillosis: A Diagnostic Challenge

Allergic bronchopulmonary aspergillosis (ABPA) is an immunologic condition that results from an allergic immune response to Aspergillus fumigatus, most often occurring in a patient with bronchial asthma or cystic fibrosis. ABPA is diagnosed by constellation of clinical, laboratory, and radiographic criteria. In the absence of typical presentation, ABPA can be misdiagnosed. Our patient presented with a 3 cm right lower lobe lung mass and sub-centimeter right upper lobe lung nodules. The clinical features led to a presumptive diagnosis of lung carcinoma. The patient underwent preoperative bronchial washing and endobronchial biopsy. The washing sample showed large amount of thick mucus containing abundant eosinophils, Charcoat-Leyden crystals, and degenerated cellular debris consistent with “allergic mucin”. These findings were initially overlooked and considered non-specific. Repeat sampling (needle biopsy) showed marked reactive pneumocyte hyperplasia in the background of inflammation, which was misdiagnosed as adenocarcinoma with lepidic growth pattern. The correct diagnosis was made only after the surgical resection of the lesion. Diagnosis of ABPA can be missed due to general unfamiliarity with this entity and its clinical presentation similar to the lung tumor. Accurate diagnosis can be derived from the bronchial washing if the features of “allergic mucin” are recognized and confirmed with microbiological examination.