Primary amebic encephalitis and granulomatous amebic encephalitis are central nervous system infections caused by free-living amebae.
They have distinctive epidemiology,
pattern of presentation,
clinical course,
pathology,
and imaging findings.
Granulomatous amoebic encephalitis (GAE),
also referred to as cerebral amoebiasis,
is caused by free-living amoebae such as Acanthamoeba spp (main cause), Balamuthia mandrillaris and Sappinia pedata. It is a distinct clinical syndrome to primary amoebic meningoencephalitis (PAM),
which is an acute illness that presents like a severe bacterial meningoencephalitis and is caused by Naegleria fowleri.
GAE has a gradual and highly variable subacute-chronic course over weeks and months.
It is known to occur in patients who are debilitated or immunocompromised by AIDS,
chemotherapy,
or steroid therapy. The clinical course is characterized by a long duration of focal neurologic symptoms unlike the rapid progression and fulminant course of patients with PAM.
The symptoms include: headache,
low fever,
seizures,
hemiparesis,
and coma leading to eventual death. It has been posited that the skin and olfactory neuroepithelium serve as portals of entry,
and occasionally,
an inflammatory process may indeed be observed at these primary foci.
Skin lesions,
such as plaques over the face, may especially be prominent in patients with GAE due to Balamuthia mandrillaris. Furthermore,
as GAE commonly coincides with other CNS infectious diseases,
the clinical presentation could be even more variable due the other associated comorbidities. Although lumbar puncture is generally contraindicated for patients who present with a focal intracranial lesion,
when CSF can be obtained,
the following may be seen: pressure slightly elevated, presence of lymphocytes and plasma cells, glucose levels are usually low, moderately high protein levels. PCR of the cerebrospinal fluid can be diagnostic.
The approach to treatment is uncertain and is based on case report-level evidence.
A variety of antifungal and antiparasitic agents may be trialled in combination.
Neurosurgical intervention may also be sought.
PAM is caused by Naegleria fowleri,
with most patients having an acute onset of symptoms with rapid progression and almost always fatal meningoencephalitis within 48–72 hours.
The affected patients are children and young adults with no immunologic compromise.
The mode of entry of these thermophilic organisms is through the olfactory tract during contact with contaminated water. It presents similarly to a severe and highly aggressive bacterial meningoencephalitis,
with common clinical features including severe headache,
high fever,
nuchal rigidity,
nausea,
vomiting,
photophobia,
cranial nerve palsies,
change in mental status,
seizures,
and clinical signs of meningeal irritation. Characteristic lumbar puncture findings include: neutrophilia, presence of red blood cells (especially as the disease progresses), markedly low glucose levels, moderately high protein levels.The approach to treatment is uncertain and is based on case report-level evidence.
A variety of antifungal and antiparasitic agents may be trialled in combination.
Prognosis is often very poor even with treatment.