Solitary Nocardia farcinica brain abscess in an immunocompetent adult mimicking metastatic brain tumor: rapid diagnosis by pyrosequencing and successful treatment.

BACKGROUND: Nocardia brain abscess carries a higher morbidity and mortality rate than other bacterial cerebral abscesses, with reported mortality rates of 55% and 20% in immunocompromised and immunocompetent patients, respectively. To prevent a delay in diagnosis and treatment, an aggressive therapeutic approach is required. In the present study, a rapid and accurate molecular diagnostic approach using pyrosequencing (PS), a semiautomated molecular genotyping method of nucleotide sequencing-by-synthesis, was performed.

CASE DESCRIPTION: A 53-year-old man developed word-finding difficulties, followed by confusion and disorientation. On examination, the patient had a mixed aphasia; the receptive component was greater than the expressive component. The remainder of his neurologic examination findings was normal. Gadolinium-enhanced magnetic resonance imaging of the brain revealed a 2.0-cm multilobular, partially cystic, peripheral-enhancing mass in the posterior left temporal-parietal region with significant vasogenic edema and localized mass effect. A detailed laboratory investigation revealed that this patient was immunocompetent. An awake left posterior temporal-parietal craniotomy with cortical motor and speech mapping, using frameless stereotactic image guidance and intraoperative real-time ultrasound, was performed. Frozen section was consistent with cerebral abscess and methenamine silver staining revealed many beaded, thin-branching gram-positive bacilli. Colonies suspicious for Nocardia sp were seen within 2 days, and PCR followed by pyrosequencing (PS) identified Nocardia farcinica.

CONCLUSIONS: We report a nocardial cerebral abscess mimicking a metastatic brain tumor, and we demonstrate that PS technology can be used for the accurate and rapid identification of N farcinica isolated from a brain abscess -- facilitating a rapid diagnosis and successful, durable treatment.