Primary amoebic meningoencephalitis

Last revised by Daniel J Bell on 13 Jun 2022

Citation, DOI, disclosures and article data

Citation:

Sharma R, Bell D, Iqbal S, et al. Primary amoebic meningoencephalitis. Reference article, Radiopaedia.org (Accessed on 19 Apr 2024) https://doi.org/10.53347/rID-53854

DOI:

https://doi.org/10.53347/rID-53854

Permalink:

https://radiopaedia.org/articles/53854

rID:

53854

Article created:

10 Jun 2017, Rohit Sharma ◉

Disclosures:

At the time the article was created Rohit Sharma had no recorded disclosures.

View Rohit Sharma's current disclosures

Last revised:

13 Jun 2022, Daniel J Bell ◉

Disclosures:

At the time the article was last revised Daniel J Bell had no financial relationships to ineligible companies to disclose.

View Daniel J Bell's current disclosures

Revisions:

8 times, by 5 contributors - see full revision history and disclosures

Systems:

Central Nervous System

Synonyms:

Amoebic encephalitis
Entamoeba histolytica encephalitis
Amoebic meningoencephalitis
Naegleriasis
Naegleria fowleri infection

Primary amoebic meningoencephalitis, also known as naegleriasis, is a rare and usually fatal acute CNS infection caused by the free-living amoeba Naegleria fowleri.

This is a distinct clinical syndrome to granulomatous amoebic encephalitis, which is a subacute-chronic illness in immunocompromised patients with a highly variable presentation that is caused by Acanthamoeba spp. (main cause), Balamuthia mandrillaris and Sappinia pedata.

Primary amoebic meningoencephalitis has a very acute presentation, with fatality usually occurring within a week of symptom onset regardless of treatment status ^1,2. 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, clinical signs of meningeal irritation and coma ^1,5.

CSF

Characteristic lumbar puncture findings include ¹:

neutrophilia
presence of red blood cells (especially as the disease progresses)
markedly low glucose levels
moderately high protein levels

Pathology

Naegleria fowleri is most commonly found in fresh and warm water sources such as lakes and hot springs, and transmission occurs due to inhalation of infested water ³. Once in the brain, PAM results in extensive damage, characterized by a purulent exudate and necrosis of the brain parenchyma, ependyma, and meninges ². The exudate usually contains a mixture of neutrophils and the amoeba itself ².

Radiographic features

Imaging findings of primary amoebic meningoencephalitis are non-specific and rarely described in the literature, but are in keeping with a hemorrhagic meningoencephalitis and its associated complications ^2,4,5:

often normal in the earliest stages (e.g. at presentation)
leptomeningeal enhancement, although diffuse subarachnoid hemorrhage is often also present
brain edema and associated hydrocephalus
multiple cerebral infa rcts
necrosis in the brain

Treatment and prognosis

The approach to treatment of naegleriasis is uncertain and based on case report-level evidence ^2,3. A variety of antibacterial, antifungal and antiparasitic agents may be trialled in combination ^2,3,5. Prognosis is often very poor even with treatment ^1-3.