Early diagnosis of primary amoebic meningoencephalitis (PAM) is critical so that treatment can be started as soon as possible. The biggest hurdle is that the disease is difficult to differentiate from bacterial or viral meningoencephalitis.
Microscopic examination
The definitive diagnosis of N. fowleri is the direct visualization of mobile trophozoites in a fresh sample of cerebrospinal fluid (CSF). Movement is rapid and directional. Their size in CSF varies from 15 to 30 microns. Cysts and the flagellate stage are not seen in CSF or other body tissues. The CSF may vary in color from grayish to yellowish-white. An increase in both red and white blood cells (predominately polymorphonuclear neutrophils) may be seen as the disease progresses, as well as an increase in protein and a decrease in glucose concentrations. The amoebae may be distinguished from other host cells by the large, round, central nucleolus.
Naegleria may also be identified from CSF smears, cultures, or brain biopsy/autopsy specimens using hematoxylin and eosin (H&E), periodic acid-Schiff (PAS), trichrome, Giemsa, or Wright-Geimsa stains. Gram stain may not be helpful, as heat fixation may destroy the amebae.
