Clinical and Radiographic Characteristics of Nocardia vs Non-Nocardia Brain Abscesses

Diagnosis and treatment of CNS nocardiosis is challenging and often delayed, which increases morbidity and mortality. The primary objective was to compare the clinical and radiographic characteristics of patients with CNS nocardiosis with non-Nocardia bacterial brain abscesses.

We performed a case-control study of patients with brain abscesses diagnosed between 1998 and 2018 at a tertiary academic center. We identified 56 patients with brain MRI demonstrating brain abscess from the institutional imaging database: 14 with culture-confirmed nocardiosis and 42 randomly selected prevalent controls with culture-confirmed non-Nocardia bacterial infection. The primary outcomes were the diagnosis of concomitant lung infection and history of immunosuppression. Secondary outcomes included abscess radiographic characteristics: multifocality, occipital lobe and/or infratentorial location, and bilobed morphology.

Compared with patients with non-Nocardia brain abscesses, patients with CNS nocardiosis were older (median 61 years [IQR 59-69] vs 48 years [IQR 34-61]; p = 0.03), more likely to be immunosuppressed [71% (10) vs 19% (8); p < 0.001), have diabetes (36% (5) vs 10% [4]; p = 0.03), or a concomitant lung infection (86% [12] vs 2% [1]; p < 0.001). Radiographically, more cases of CNS nocardiosis exhibited multifocal abscesses (29% [4] vs 2% [1]; p = 0.01), which were located in the infratentorial (43% [6] vs 10% (4); p = 0.01) or occipital (36% [5] vs 5% [2]; p = 0.008) regions and had a bilobed (as opposed to unilobed) morphology (79% [11] vs 19% [8]; p < 0.001). Blood and CSF cultures were negative in most of the cases and controls, whereas neurosurgical specimen culture yielded a diagnosis in 100% of specimens.

Patients with CNS nocardiosis were more likely to be older, have a history of diabetes or immunosuppression, or have a concomitant lung infection compared with those with non-Nocardia brain abscesses. Abscesses because of CNS nocardiosis were more likely to be multifocal, affect the infratentorial region or occipital lobe, or have a bilobed appearance. Neurosurgical specimen culture was most likely to yield a diagnosis for both Nocardia and non-Nocardia abscesses. The combination of clinical and imaging findings may suggest CNS nocardiosis and inform early initiation of targeted empiric treatment.