Abstract
RATIONALE: Pulmonary nocardiosis (PN) is an opportunistic infectious disease caused by Nocardia of the lungs, which lacks specificity in clinical symptoms and imaging, is rare in individuals with normal immune function, and is highly prone to clinical misdiagnosis and missed diagnosis. PATIENT CONCERNS: A 55-year-old woman with normal immune function was admitted to the hospital due to a cough and expectoration for more than 20 days. DIAGNOSES: Chest computed tomography revealed a mass in the left hilum and obstructive atelectasis in the lingular segment of the left upper lobe. Initially suspected to be a malignant tumor, bronchoscopy with pathological examination suggested inflammation. Finally, metagenomic next-generation sequencing of pathological tissue confirmed PN. INTERVENTIONS: After discharge, the patient regularly took trimethoprim-sulfamethoxazole for anti-infective treatment. OUTCOMES: Regular follow-ups with the patient revealed that subsequent chest computed tomography scans showed a gradual reduction in the extent of the lesions, and the patient demonstrated a good clinical response and radiological improvement. LESSONS: This case highlights the diagnostic complexity of PN. The radiological manifestations are diverse, commonly including pulmonary consolidation, nodules, and cavities, making it difficult to differentiate from other diseases. Clinicians need to be vigilant and find appropriate testing methods to improve the diagnostic rate of PN.