The trophozoites of Acanthamoebae tend to be 8-12 microns in greatest dimension in tissue sections. The cytoplasm is highly vacuolated and the nucleus has a large round dense karyosome with a halo around it. The trophozoites of Balamuthia are larger, 15-35 microns in greatest dimension, with a less prominent nuclear karyosome. Morphological criteria are inadequate, while thermophilic character, pH dependency and even virulence in infected mice are not unambiguous features of pathogenicity of the different strains. Monoclonal antibodies are also available for immunofluorescence microscopy testing, as illustrated in this case, but it is not practical for most hospital laboratories to keep these reagents, which would usually outdate before they were used, and small hospital laboratories may not have no facility for fluorescence microscopy.
Brain biopsies are commonly diagnostic.
Direct identification or isolation of the protozoa from the central nervous system provides a specific diagnosis. Granulomatous amebic encephalitis usually has a prolonged clinical course and early diagnosis by brain biopsy holds the hope of successful treatment because there are multiple drugs, such as ketoconazole, miconazole, 5-flucytosine and pentamidine, effective against the causative organisms in vitro. Free-living amebic infections. Orrison WW Jr. Granulomatous amebic encephalitis caused by acanthamoebae. Cerebral amebiasis in the acquired immunodeficiency syndrome.