DIAGNOSIS: Listerial Rhombencephalitis
Listeria monocytogenes is a non-spore forming, motile, facultative intracellular, gram-positive bacteria, which causes sporadic food-borne outbreaks and life-threatening infections in immunocompromised hosts (3,13). Listerial meningoencephalitis was first described in 1934 (4), and is now recognized as a common cause of central nervous system (CNS) infection in patients with impaired cellular immunity. Rhombencephalitis or brain stem encephalitis is an unusual form of CNS listeriosis first described in1957 by Eck (8). The term rhombencephalitis refers to the initial involvement of the pons and medulla, the embryological derivatives of the rhombencephalon or hindbrain. This peculiar anatomic distribution is akin to the common listerial zoonosis of ruminants called “circling disease”. Affected animals present with a stereotyped circling motion towards the side of unilateral facial paralysis caused by a brainstem abscess. Recently, Antal et al.(2) have elegantly reproduced this pathologic entity in a murine model, with compelling evidence of the intra-axonal spread of L. moncytogenes into the brainstem after inoculation of the facial nerve and muscle.
Patients with rhombencephalitis described in the literature to date, have historically been immunocompetent adults (1,3,6,8,9,11,12,13,14). The source of infection, when identified, has been by and large a dairy product (14). Headache, vomiting, fever, and ill-defined neurologic symptoms characterize a prodromal stage of one or two week’s duration (3,14). Patients then develop the full spectrum of brainstem symptomatology, which is customarily a combination of cranial nerve palsies, cerebellar and long-tract motor and sensory deficits, and recently described “musical” auditory hallucinosis (6). Nuchal rigidity and other meningeal signs are frequently absent (3,14). Examination of CSF is usually normal, but may show slight pleocytosis, increased protein and decreased glucose levels (14). CSF and blood cultures are reported to be positive in 40% and 60% of patients, respectively (3). MRI typically shows a nodular ring-enhancing lesion, which appears hyperintense on the corresponding T2-weighted sequences (1,3,9,11,12). This combination of MRI findings are atypical for a brainstem infarct or primary glial neoplasm, and should raise the possibility of brainstem encephalitis. Stereotactic aspiration of a brainstem abscesses in expert hands (7,10,12,13) has proven to be diagnostic. Rapid therapeutic intervention prevents caudal extension of the infection into the lower medulla, which can lead to cardiopulmonary arrest and death (3). We found no reports in the literature of listerial rhombencephalitis following dental surgery. We can only speculate what role if any, a minor dental procedure played in this patient’s infection.
Post operatively, the patient was started on broad-spectrum intravenous antibiotics. On follow up, culture isolates were speciated as L. monocytogenes using a chemiluminescent-labeled DNA probe assay (5). A repeat MRI scan, performed three days after the biopsy demonstrated the abscess cavity was significantly evacuated by the biopsy. The patient was discharged home on ampicillin, trimethoprim sulfamethoxazole and oral corticosteroids, her only neurologic complaint was a mild decrease of sensation over the right perioral aspect of the face.
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Contributed by Rafael Medina-Flores, MD, Anand Germanwala, MD, J. Thomas Molina, MD, PhD, Carolyn C Meltzer, MD, and Clayton A Wiley, MD, PhD