Encephalopathy in the emergency department. A case of Listeria monocytogenes

Introduction: Encephalopathy in the emergency department represents a diagnostic challenge due to its multifactorial etiology, which includes metabolic, infectious, and vascular causes. Listeria monocytogenes meningitis is a serious infection with high morbidity and mortality, which mainly affects older adults and immunosuppressed individuals. Clinical case: A 65-year-old male patient with multiple comorbidities was admitted to the emergency department due to altered consciousness, fever, headache, vomiting, and a seizure. Physical examination revealed hypoglycemia, hypernatremia, hyperammonemia, uremia, hypertension (180/90 mmHg), and hypoxia (saturation 80%). Metabolic alterations were corrected, empirical antibiotic therapy (vancomycin, ceftriaxone, dexamethasone) was initiated, and a lumbar puncture was performed. CSF culture confirmed Listeria monocytogenes meningitis, and treatment was adjusted to ampicillin and gentamicin. The patient's outcome was favorable. Discussion. This clinical case illustrates the diagnostic complexity of encephalopathy in patients with multiple comorbidities, where metabolic, infectious, and hypertensive factors converge. The identification of Listeria monocytogenes as the etiologic agent by CSF culture underscores the need to include this bacterium in the differential diagnosis of meningoencephalitis in older adults with risk factors, especially in settings of relative immunosuppression. Conclusions: The patient's favorable outcome was possible thanks to a comprehensive and timely approach, which combined the stabilization of critical metabolic alterations, hemodynamic monitoring, and the early initiation of targeted antibiotic therapy. This case reinforces the importance of maintaining a high index of clinical suspicion in atypical neurological presentations and of using complementary diagnostic tools such as lumbar puncture, especially when classic signs may be masked. In the emergency setting, this systematic and multidisciplinary approach is essential to reduce morbidity and mortality associated with treatable infectious causes of encephalopathy, such as neurolisteriosis.