Secondary Immunodeficiency and Non-cystic Fibrosis Bronchiectasis.

Bronchiectasis is a chronic respiratory disease characterized by abnormal dilation of the bronchi that causes cough, sputum, and recurrent infections. As it may be associated with various respiratory or systemic diseases, a critical aspect of managing bronchiectasis is to identify the underlying cause. Immunodeficiency is a rare but important cause of bronchiectasis, and its treatability is a significant trait for bronchiectasis management. While primary immunodeficiencies in bronchiectasis are well recognized, secondary immunodeficiencies remain under-reported and under-researched. Secondary immunodeficiencies may result from various diseases and conditions, such as hematologic malignancies, human immunodeficiency virus infection, renal transplantation, or the use of immunosuppressive drugs, and may contribute to the occurrence of bronchiectasis. Recurrent pulmonary and/or extrapulmonary infections in bronchiectasis may indicate the presence of secondary immunodeficiency in patients with these underlying conditions. For treatment, examining the underlying condition, managing bronchiectasis adequately, and prophylactic antibiotics (e.g., macrolide) and/or supplementary immunoglobulin G therapy may provide potential benefits. Considering the projected increase in the prevalence of secondary immunodeficiencies and bronchiectasis, future guidelines and research on the diagnosis and optimized treatment are needed.