An Atypical Presentation of Allergic Bronchopulmonary Aspergillosis.

Allergic bronchopulmonary aspergillosis (ABPA) is an immune-mediated hypersensitivity reaction to Aspergillus fumigatus, usually occurring in patients with asthma or cystic fibrosis. Presentation with lobar atelectasis or pleural effusion is rare and can mimic malignancy. We report a 57-year-old man without pre-existing lung disease who presented with cough and progressive dyspnea unresponsive to antibiotics. Imaging showed left upper lobe atelectasis with pleural effusion and subcarinal lymphadenopathy. Bronchoscopy revealed complete obstruction of the left upper lobe bronchus by thick mucus plugs; histopathology and culture confirmed A. fumigatus. Laboratory testing showed marked eosinophilia, elevated total immunoglobulin-E (IgE), and positive A. fumigatus precipitins, findings compatible with the diagnosis of ABPA. Treatment with oral prednisolone and itraconazole led to full clinical and radiological recovery, with sustained remission under inhaled corticosteroid/long-acting β₂-agonist therapy. This case highlights an uncommon presentation of ABPA with pleural effusion and lobar collapse and emphasizes the importance of considering ABPA in the differential diagnosis of unexplained or eosinophilic pleural effusions.