Amebic Infections of the Brain

Sumit Karia MD

The Common Vein Copyright 2010


There are 3 amebic parasites known to cause CNS infections – Naegleria fowleri, Acanthamoeba spp., and Entamoeba spp, though such infections are very rare.

Infections arise when the patient swims in water contaminated by these amebae. Trophozoites or cysts penetrate the nasal mucosa and are phagocytosed by cells of the olfactory neuroepithelium, ascending through the olfactory nerves, hence reaching the brain. The body responds with an intense phagocytic activity and proteolysis, that causes damage. This results in acute purulent meningitis, necrotizing hemorrhagic encephalitis and vasculitis. In certain cases, granulomas can develops, originating what is called graulomatous amebic encephalitis, where there is a constellation of the 3 mentioned forms.

Patients present with symptoms of meningitis – high-grade fever, headache, stiff neck, seizure, and altered mental status; if left untreated it can originate increased intracranial pressure and cerebral herniation.

Diagnosis is made through examination of the CSF. As with bacterial meningitis, polymorphonuclear leukocytosis is seen with increased protein and low glucose levels. Trophozoites may be seen.

Neuroimaging is usually normal in the meningitis form, though multifocal contrast-enhancing lesions may be seen, which tend to affect the diencephalon, mesencephalon and posterior fossa. In the granulomatous encephalitis, space-occupying lesions are seen, which care located in the subarachnoidal space.

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