A case of primary amebic meningoencephalitis. Light and electron microscopy, and immunohistologic studies.

A 56-year-old alcoholic developed primary meningoencephalitis and died 3 weeks later. Autopsy revealed multiple areas of necrosis and acute and granulomatous inflammation in the brain and pancreas. Trophozoites and cysts were discovered in the brain and trophozoites alone in the pancreas. Morphologic studies revealed some parasitic features described as characteristic for Naegleria, but clinical, histological and immunohistological features favored in Acanthamoeba infection. This study calls for caution in the use of pure morphological criteria for the differential diagnosis of Naegleria and Acanthamoeba in humans. Cultural characteristics, immunohistology and serologic tests are probably more reliable for differentiating these parasites.