A 38-year-old woman presented with a 1-month history of progressive cough and phlegm. She was an office worker. She denied the presence of comorbidities including diabetes, renal disease, malignancy and acquired immune deficiency syndrome. She underwent chest CT scan (figure 1A) 2 weeks before admission, having been taking moxifloxacin treatment for 12 days without improvement in symptoms. A repeat CT scan at admission showed significant progression of the lung lesions compared with previous imaging (figure 1B). Sputum culture was negative. Laboratory investigations revealed NK cells, CD4+, CD8+ lymphocytes and the CD4+/CD8+ lymphocytes ratio, serum interferon-γ, TNF-α, immunoglobulins (IgG, IgA and IgM), and complement components 3 and 4 detections were all in the normal range. A bronchoscopy showed mucoid impactions completely obstructed the anterior basal segment of the right lower lobe (figure 1C). Radial endobronchial ultrasound (EBUS) was used to detect the lesion in the bronchial …