Rare Pathogens of Central Nervous System: a Systematic Literature Review and Report of Two New Cases of Cerebral Abscesses Due to Gemella morbillorum

To evaluate and characterize cases of brain abscess in immunocompetent patients due to Gemella morbillorum, an opportunistic Gram-positive coccus. Two cases of brain abscess due to this pathogen which occurred at the authors’ native institution in 2013 and 2016 were analyzed. Moreover, a literature search regarding brain abscess surgically treated due to this pathogen was performed in PubMed database, following PRISMA statement. The final review comprised ten articles for a total of 11 patients—all immunocompetent—with a median age of 50.2 years (range 28–77); almost total were males. Neurological deficits and fever were the most common initial signs; seizures were present only in two cases. Surgical treatment was based on craniotomy and excision in six cases; the remaining five underwent stereotactic aspiration. The antibiotic initial therapy was intravenous in all cases. The average duration of therapy was of six weeks with a minimum of four and maximum of ten. One patient died, while in the other cases, a complete or partial regression of presenting symptoms and disappearing of MRI signs at intermediate follow-up were obtained. In eight patients (72%), it was possible to identify a primary infection or a predisposing factor (as cardiac diseases or septic arthritis). G. morbillorum is an emerging pathogen involved in brain abscesses. Even if it is infrequently reported, the identification of specific characteristics that may increase its neurotropism and virulence also in immunocompetent patients can help to better understand such a rare pathology.