Case Presentation: A 26-year-old male with no significant history presented with two days of fevers, headaches, myalgias, and confusion. On arrival to the hospital, he was febrile to 104.5F, responsive to commands but lethargic. He was warm, diaphoretic, with no nuchal rigidity and negative Kernig and Brudzinski signs. Neurological and ophthalmologic exams were noncontributory. Laboratory testing showed a neutrophilic predominant leukocytosis (WBC 24.4 K/uL) and lactate of 3.9 mmol/L without significant electrolyte abnormalities. CT head was unremarkable. Empiric ceftriaxone, vancomycin, and acyclovir were started following unsuccessful lumbar puncture. He remained febrile and his mental status deteriorated with waxing and waning delirium. On reexamination he had left-sided anisocoria with a dilated and unresponsive pupil. He continued to decompensate and became obtunded requiring intubation for airway protection. Lumbar puncture was performed, and CSF and blood cultures grew Listeria monocytogenes. Antibiotics were switched to ampicillin and gentamicin. The patient defervesced and was extubated after 4 days. He clinically improved and was without cognitive or motor deficits. However, he had persistent anisocoria, ptosis, horizontal diplopia, and mild hearing loss. MRI/MRA brain with contrast showed a cytotoxic lesion of the corpus callosum, leptomeningeal and pachymeningeal enhancement, and possible ventriculitis. MRI orbits with contrast was unremarkable. He completed 7 days of gentamicin and was discharged home to complete 4 weeks of ampicillin. The source of the Listeria was not identified.

Discussion: Listeria monocytogenes is the third most common causative organism for community acquired bacterial meningitis [1,2]. Listeria meningitis is more common in immunocompromised and elderly patients, but can rarely occur in healthy adults [3-6]. As in this patient’s case, Listeria meningitis presents similarly to more common etiologies of meningitis and patients often do not initially receive appropriate antibiotic coverage. This patient rapidly developed blurry vision, worse in left gaze improving in right gaze, and photophobia. Ophthalmological exam revealed a left dilated, minimally reactive pupil, left ptosis, and alternating esotropia with a V pattern. These findings were consistent with a pupil-involving third nerve palsy, possibly secondary to meningitis leading to irritation of the nerve, mass effect from increased ICP, or microvascular changes affecting the course of the nerve. A review of the literature elucidated that of the few healthy adults who develop Listeria meningitis there are even fewer reports of associated CNIII palsy. An observational study found that of 59 patients with Listeria meningoencephalitis, only 1 had CNIII findings that were still present at 3 months [7]. Cao et al. reported 5 healthy younger adults with Listeria meningitis, only 1 of whom had diplopia [8]. It is unclear how long these visual deficits last, given that the available cases do not report long term outcomes.

Conclusions: Listeria monocytogenes is a rare but potentially devastating cause of bacterial meningitis in patients without known risk factors. Our case discusses a low-risk patient who developed Listeria meningitis with resulting pupil-involving third nerve palsy. Patients without known risk factors likely will not initially receive appropriate coverage for Listeria which may lead to adverse sequelae including cranial nerve injury and higher mortality.