Pulmonary Nocardiosis in Diverse Clinical Settings: A Case Series Highlighting Diagnostic Challenges and Radiological Spectrum.

Abstract

ABSTRACT Pulmonary nocardiosis is an uncommon but potentially serious infection caused by aerobic actinomycetes of the genus Nocardia. It predominantly affects individuals with impaired immunity or underlying structural lung disease, but can also occur in apparently immunocompetent hosts. The clinical and radiological features often overlap with tuberculosis and fungal infections, particularly in endemic regions, leading to frequent misdiagnosis and delay in appropriate therapy. We present a series of three patients with microbiologically confirmed pulmonary nocardiosis, each representing different clinical backgrounds. The first case involved a middle-aged male with poorly controlled diabetes mellitus presenting with chronic cough and bilateral pulmonary infiltrates. Imaging revealed patchy peribronchial opacities, and bronchoalveolar lavage (BAL) demonstrated filamentous, weakly acid-fast organisms on modified acid-fast staining. The second case was an elderly female with underlying bronchiectasis who presented with increased cough and expectoration; imaging showed bronchiectatic changes with superimposed infiltrates, and BAL confirmed Nocardia infection. The third case involved an elderly male with recent immunosuppressive therapy who presented with acute respiratory symptoms and radiological evidence of multifocal consolidation; microbiological evaluation confirmed nocardiosis. All patients were treated with appropriate antimicrobial therapy, including trimethoprim-sulfamethoxazole as the backbone, with additional agents such as imipenem or linezolid in selected cases. Clinical improvement was observed in patients who adhered to therapy, with symptomatic relief and partial radiological resolution on follow-up. This case series underscores the varied clinical presentation and imaging spectrum of pulmonary nocardiosis. Diabetes mellitus, structural lung disease, and immunosuppressive therapy emerged as key predisposing factors. The condition often mimics tuberculosis or bacterial pneumonia, making microbiological confirmation using modified acid-fast staining crucial. Early diagnosis and prompt initiation of appropriate therapy significantly influence patient outcomes. Pulmonary nocardiosis should be considered in patients with nonresolving pulmonary infiltrates, especially in the presence of risk factors such as diabetes, bronchiectasis, or immunosuppression. A high index of suspicion, combined with timely microbiological diagnosis and appropriate antimicrobial therapy, is essential to improve prognosis and reduce morbidity.