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Acute PAM presents 1-7 days (median 5 days) after exposure. Presenting symptoms might include severe headache, fever, vomiting, and seizures. Other symptoms such as photophobia, mental status abnormalities, lethargy, dizziness, ataxia, cranial nerve palsy, hallucinations, and delirium have been reported. Findings on exam may include meningeal signs and focal neurologic deficits. Signs and symptoms mimic those of bacterial meningitis, especially in the early stages. In some cases, abnormalities in taste or smell, nasal obstruction, and nasal discharge have been observed.

PAM progresses rapidly and frequently leads to coma and death in 1-12 days (median 5 days) after symptom onset. Autopsy findings include hemorrhagic necrosis of the olfactory bulbs and cerebral cortex. In contrast, other free-living amebae (Acanthamoeba spp. and Balamuthia) cause mostly sub-acute or chronic granulomatous amebic encephalitis (GAE), with a clinical picture that can include headaches, altered mental status, and focal neurologic deficits. GAE generally progresses more slowly than PAM and death usually occurs several weeks to months after symptom onset.

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  • Page last reviewed: November 14, 2013
  • Page last updated: November 14, 2013 The U.S. Government's Official Web PortalDepartment of Health and Human Services
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