Rare Non-Tuberculous Mycobacterium as a Cause of Necrotizing Pneumonia: Case Report of Pulmonary Infection by Mycobacterium Nebraskense

Non-tuberculous mycobacteria (NTM) are environmental bacilli with variable pathogenic potential, recognized as emerging causes of chronic pulmonary infections. Mycobacterium nebraskense, described in 2004, is a slow-growing and rare NTM, usually isolated from respiratory secretions. Reports of true pulmonary infection caused by this species are scarce; clinical presentations are nonspecific, and diagnosis is often delayed, making targeted treatment difficult. We report the case of a 53-year-old female patient, previously healthy, admitted with asthenia, myalgia, and prolonged fever (>2 weeks). She was initially treated as pneumonia with ceftriaxone and azithromycin for 5 days, without clinical response. Chest CT showed extensive heterogeneous consolidation in the left lung (upper lobe, lower lobe, and lingula), with areas of ground-glass opacity, gas-filled cavitations, and calcifications, as well as opacities in the right upper lobe, the largest measuring 1.8 cm. Laboratory tests showed C-reactive protein of 310 mg/L, leukocytosis of 29,200/mm³ with neutrophilia (89%), and negative HIV. Considering necrotizing pneumonia, cefepime and clindamycin were started for 14 days, without improvement. On day 21, due to clinical worsening, a regimen with meropenem, linezolid, and amikacin was instituted. On the same day, bronchoscopy with bronchoalveolar lavage was performed for cultures, histopathology, and oncotic cytology. The patient progressed with decreased level of consciousness and respiratory failure, requiring mechanical ventilation. Despite intensive support, she died on the 32nd hospital day. After death, the bronchoalveolar lavage pathology revealed exulcerative-suppurative bronchiolitis, with no neoplastic cells, and culture positive for Mycobacterium nebraskense. The rarity of the mycobacterium and the nonspecific clinical presentation hindered early diagnosis, resulting in therapeutic failure. This case reinforces the importance of considering NTM in the differential diagnosis of necrotizing pneumonias with atypical course, even in immunocompetent patients.