Nocardia pneumonia in a patient with granulomatosis with polyangiitis receiving immunosuppressive therapy: Importance of culture test and identification of the species

Abstract

Here, we report a case of nocardia pneumonia in a 68-year-old man with granulomatosis with polyangiitis（GPA）receiving corticosteroid and rituximab therapy for 8 months. In March 2017, he was admitted for pneumonia presenting with consolidation on CT images. Additionally, the cytomegalovirus antigenemia test was positive. Tazobactam/Piperacillin and Ganciclovir were not effective. Although exacerbation of GPA was suspected because of his bloody sputum and bronchoalveolar lavage fluid（BALF）, he was finally diagnosed with nocardia pneumonia based on the culture results of BALF. One week after his admission, the chest CT images revealed a cavitation in the consolidation in the left lower lobe. However, after initiating Imipenem and Linezolid, which were selected based on the results of antimicrobial susceptibility testing, his clinical condition promptly ameliorated, and the cavitary lesion and pneumonia gradually regressed. The antibiotic treatment was continued for 6 months without significant side effects, and no signs of recurrence were observed. Subsequentially, Nocardia farcinica was identified on 16S ribosomal RNA sequencing analysis of his cultured BALF. Nocardia is one of the agents responsible for opportunistic infections in immunocompromised individuals. The diagnosis of nocardia pneumonia is often difficult because CT findings are non-specific and Nocardia may not be detected in sputum. Therefore, the culture of BALF is considered useful for the diagnosis. Furthermore, clinical features and susceptibility to antimicrobial agents in Nocardia sp. can vary. Accurate identification of the Nocardia species is important for optimal patient management.