Granulomatous amoebic encephalitis

Last revised by Andrew Murphy on 31 Jul 2022

Granulomatous amoebic encephalitis (GAE), also referred to as cerebral amoebiasis, is a rare and usually fatal subacute-chronic CNS infection in immunocompromised patients caused by free-living amoebae such as Acanthamoeba spp. (main cause), Balamuthia mandrillaris and Sappinia pedata.

This is a distinct clinical syndrome to primary amoebic meningoencephalitis, which is an acute illness that presents like a severe bacterial meningoencephalitis and is caused by Naegleria fowleri.

Granulomatous amoebic encephalitis has a gradual and highly variable subacute-chronic course over weeks and months 1-6. Patients with granulomatous amoebic encephalitis have been described with symptoms that include: headache, low fever, seizures, hemiparesis, and coma leading to eventual death 2. This presentation is often more aggressive in cases due to Balamuthia mandrillaris when compared to cases due to Acanthamoeba spp. 4

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 5. Skin lesions, such as plaques over the face, may especially be prominent in patients with granulomatous amoebic encephalitis due to Balamuthia mandrillaris 4.

Furthermore, as granulomatous amoebic encephalitis 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 3:

  • 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 

Multifocal parenchymal lesions characterized by foci of chronic granulomatous inflammation centered around arteries and veins and also infiltrating the meninges 1,2. Trophozoites and cysts may be found in and around walls of affected blood vessels and also in areas relatively free of inflammation 1,2.

Imaging findings are non-specific and are rarely described in the literature, but can include the following brain lesions 6:

  • multiple parenchymal lesions
  • pseudotumoral lesions
  • meningeal exudates
  • hemorrhagic infarcts (more common in Balamuthia mandrillaris)
  • necrosis (more common in Balamuthia mandrillaris)

The approach to treatment is uncertain and is based on case report-level evidence 6,7. A variety of antifungal and antiparasitic agents may be trialled in combination 6,7. Neurosurgical intervention may also be sought 6.

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