Imaging characteristics, yield of computed tomography, and clinical outcomes of central nervous system nocardiosis

BACKGROUND: Nocardia frequently disseminates to the central nervous system (CNS). Few studies have described brain imaging characteristics of these infections or compared findings of computed tomography (CT) and magnetic resonance imaging (MRI). METHODS: We conducted a retrospective cohort study of adults diagnosed with CNS nocardiosis between November 2011 and April 2022 and underwent brain MRI. We aimed to describe common brain imaging characteristics, compare the diagnostic yield of brain CT and MRI, and describe clinical outcomes. RESULTS: 52 patients were diagnosed with CNS nocardiosis, of which 26 also underwent brain CT. Most patients (N = 43; 82.7%) were receiving immunosuppressing medication, had concurrent pulmonary involvement (N = 45; 86.5%), and the most common species was N. farcinica (N = 19; 36.5%). 50% had CNS symptoms. The most common radiographic characteristics were supratentorial involvement (N = 50; 96.2%), multiple lesions (N = 31; 59.6%), and bihemispheric involvement (N = 30; 57.7%). Of 26 with both imaging modalities, 5 (19.2%) did not have signs of CNS nocardiosis on CT. These patients had smaller CNS lesions (median 0.6 versus 1.8 cm; p = 0.005) and more often had multiple brain lesions or bihemispheric involvement (both: 100% versus 47.6%; p = 0.053). Twelve (23.1%) patients died within 12 months of diagnosis, though abnormal CT and CNS lesion ≥ 1 cm were not associated with mortality. Of 33 who completed therapy, 3 (9.1%) and 2 (6.1%) patients had residual neurologic deficits or post-treatment recurrence, respectively. CONCLUSIONS: CNS nocardiosis commonly presents with multiple, supratentorial brain lesions. About 20% of patients will have a normal brain CT, usually those with multiple small lesions.