Histopathologic spectrum and immunohistochemical diagnosis of amebic meningoencephalitis

Abstract

Traditionally, Naegleria fowleri infections are labeled primary amebic meningoencephalitis because of prominent meningeal neutrophilic inflammation. Acanthamoeba spp. and Balamuthia mandrillaris are labeled granulomatous amebic encephalitis because of parenchymal granulomatous inflammation. We compared histopathologic and immunohistochemical features of 18 cases with central nervous system free-living ameba infections. Immunohistochemical assays using polyclonal antibodies that reacted specifically against each genus identified 11 patients with Balamuthia infection, four with N. fowleri, and three with Acanthamoeba. Immunohistochemical assays highlighted the presence of trophozoites that were difficult to identify with hematoxylin and eosin stains in areas of necrosis or where macrophages were abundant. Immunohistochemical assays also demonstrated the presence of granular antigens inside macrophages and blood vessel walls. Amebic cysts were observed in three patients with Acanthamoeba infection and in three with Balamuthia. Patients with Acanthamoeba infection showed granulomatous inflammation. Patients with Naegleria infection had neutrophilic inflammation. Balamuthia infections showed a spectrum of inflammation that ranged from primarily neutrophils to granulomas. Meningitis was present in 88% of cases. Immunohistochemical assays were useful to demonstrate the presence of granular antigens and confirmed the genus of the ameba. The spectrum of inflammation in cases of Balamuthia meningoencephalitis is broader than previously described. The term amebic meningoencephalitis describes better the histopathologic findings than the currently used classification of primary amebic meningoencephalitis and granulomatous amebic encephalitis.

Best Cases from the AFIP:Balamuthia mandrillarisAmebic Meningoencephalitis

“…Although classically described as a granulomatous amebic meningoencephalitis, the findings are often variable and can be primarily neutrophilic in appearance with little or no granuloma formation (3,(9)(10)(11)(12). At microscopic examination with hematoxylin-eosin (H-E) staining, amebic trophozoites are often demonstrated within the infected parenchymal tissue and perivascular spaces (9,12).…”

Diagnosing Balamuthia mandrillarisEncephalitis With Metagenomic Deep Sequencing

“…Amoebic encephalitis can show various histologic patterns, and in this case no granulomatous component was seen in the brain biopsy specimen; Balamuthia in particular is known to present with a range of inflammatory patterns. 17, 18 To our knowledge, this is the first time that an ocular infection with B. mandrillaris has been described. An unsuccessful attempt was made to culture B. mandrillaris from the CSF, but no attempt at amoebic culture was made from the remaining vitreous fluid given its small volume (i.e., 30 uL) and because it had been frozen for an extended period of time in a −70°C freezer.…”

Autoimmunity in the Mediation of Granulomatous Amoebic Encephalitis: Implications for Therapy

“…Alternatively, periodic acid-Schiff's stain and Gomori-methenamine silver stain can be used to stain tissue sections in which, cysts appear red whereas tissues appear black in color (Marciano-Cabral & Cabral, 2003). Other specialized techniques employed to demonstrate the presence of amoeba are transmission electron microscopy and immunofluorescent or immunoperoxidase staining (Willaert & Stevens, 1976, Stevens, et al, 1977, McKellar, et al, 2006, Guarner, et al, 2007. However, because most Acanthamoeba spp.…”