A Complicated Case of Nocardia Brain Abscess for Differential Diagnosis

Background: Nocardia brain abscess is rare and has uncertain clinical features. Radiological differential diagnosis based on the metabolic feature of Nocardia is discussed. Case description: A 73-year-old man presented with a history of otitis media and was treated with antibiotics for 2 weeks. Computed tomography (CT) and magnetic resonance imaging (MRI) demonstrated an irregular ring-enhancement mass in the left cerebellar hemisphere. This lesion presented as a homogeneous high-intensity area in diffusion-weighted MRI. We also found decreased N-acetyl-aspartate (NAA) peak and increased choline and lipid peaks in proton MR spectroscopy ((1)H-MRS). We performed an aspiration. Nocardia asiatice in the mass lesion was found by genetic analysis. The patient was treated with a sulfamethoxazole/trimethoprim (ST) mixture and minocycline (MINO) intravenously for 6 months. There has been no recurrence for 2 years. Conclusions: To our knowledge, this case is the first case of Nocardia aslatica brain abscess in Japan. We considered these MRS findings to be compatible with Nocardia brain abscess as mainly observed in aerobic metabolism. But we also detected a lactate peak in the abscess. Further research is required.