Early diagnosis of primary amoebic meningoencephalitis (PAM) is critical in order 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.
The definitive diagnosis of N. fowleri is the detection of mobile trophozoites in a fresh sample of cerebrospinal fluid (CSF). Movement is rapid and directional. Their size varies from 10 to 25 microns. Cysts and the flagellate stage are not seen in CSF or other body tissues. The CSF may vary in color from a 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.