Central nervous system involvement by Listeria monocytogenes usually presents as meningitis, meningoencephalitis or, less frequently, rhombencephalitis. Listerial brain abscesses are rare. Moreover, only 5-8% of listerial bacteremia is complicated by infective endocarditis (IE). A 70-year-old man with chronic immune thrombocytopenia (ITP) presented to our emergency department with acute onset of altered mental status and right-sided weakness. He was afebrile, with no heart murmurs or peripheral IE stigmata. Neurologic examination showed disorientation, expressive aphasia, and right-sided hemiparesis. Laboratory findings were unremarkable except for leukocytosis and hyponatremia. Brain MRI showed an irregular rim-enhancing lesion in the left frontal lobe, suspicious for a high-grade glial neoplasm. The lesion was excised, and he was started empirically on vancomycin, ceftriaxone, and metronidazole. After blood cultures grew Listeria monocytogenes, antibiotics were de-escalated to ampicillin and gentamicin. Echocardiography showed mitral valve vegetation. By Day 6, his mental status had improved. On Day 9, he was discharged to our inpatient rehabilitation center to complete six weeks on IV ampicillin and IV gentamicin. Pathology of the brain mass was subsequently reported as a listerial brain abscess. Chronic treatment with high-dose oral glucocorticoids and pre-existing ITP have been independently implicated as predisposing factors in listerial brain abscess. There is a propensity to misdiagnose listerial brain abscess as an intracranial neoplasm due to similar clinical/imaging findings. In addition, Listeria monocytogenes is an atypical cause of IE. Therefore, a high index of suspicion is necessary for early recognition and successful treatment of listerial brain abscess and listerial endocarditis in high-risk patients.

INTRODUCTION: Listeria monocytogenes, an intracellular gram-positive bacillus, is a ubiquitous foodborne pathogen that causes Listeriosis. Its clinical spectrum ranges from mild, self-limiting gastroenteritis in immunocompetent individuals to severe, life-threatening, invasive disease affecting persons at the extremes of age, pregnant women, and individuals with cell-mediated immunodeficiencies. Central nervous system involvement by is commonpresenting as meningitis, meningoencephalitis or, less frequently, rhombencephalitis. Listerial brain abscesses are rare. Moreover, only 5-8% of these infections are complicated by infective endocarditis (IE). CASE PRESENTATION:A 70-year-old Caucasian man with chronic immune thrombocytopenia (ITP) presented to the ED with acute onset of altered mental status and right-sided weakness. He was afebrile, with no heart murmurs or peripheral stigmata of IE. Neurologic exam findings included disorientation, expressive aphasia, and right-sided hemiparesis. Laboratory findings were unremarkable except for leukocytosis and hyponatremia. Brain MRI showed an irregular rim-enhancing lesion in the left frontal lobe with surrounding edema and midline shift. The lesion was excised with adjacent necrotic tissue and frozen sections were highly suspicious for a high-grade glial neoplasm. He was started empirically on vancomycin, ceftriaxone and metronidazole. Eventually, the organism was identified as Listeria monocytogenes from two sets of blood cultures; hence, antibiotics were deescalated to ampicillin and gentamicin. Transesophageal echocardiography (TEE) showed mitral valve vegetation. The patient developed fever on day 4; by day 6, he began to defervesce and showed improvement in mental status. On day 9, he was discharged to the inpatient rehabilitation center to complete a total of 6 weeks on IV ampicillin and IV gentamicin. Pathology of the brain mass was subsequently reported as listerial brain abscess with no evidence of malignancy.DISCUSSION: Chronic treatment with high-dose oral glucocorticoids and pre-existing ITP have been independently implicated as predisposing factors in listerial brain abscess. There is a propensity to misdiagnose listerial brain abscess as an intracranial neoplasm due to similar clinical/imaging findings, especially when fever is absent at presentation. In addition, Listeria monocytogenes is an atypical cause of IE. Our patient had no pre-existing structural or valvular heart disease, but he satisfied two major diagnostic criteria for IEtwo separate positive blood cultures of Listeria monocytogenes and a TEE demonstrating mitral valve vegetation.CONCLUSIONS: A high index of suspicion is necessary for early recognition and successful treatment of listerial brain abscess and listerial endocarditis in high-risk patients.