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Granulomatous Amebic Encephalitis


Chelsea Marie

, PhD, University of Virginia;

William A. Petri, Jr

, MD, PhD, University of Virginia School of Medicine

Reviewed/Revised Dec 2022

Granulomatous amebic encephalitis is a very rare, generally fatal subacute central nervous system (CNS) infection caused by Acanthamoeba species in immunocompromised or debilitated hosts or by Balamuthia mandrillaris.

Acanthamoeba species and Balamuthia mandrillaris are present worldwide in water, soil, and dust. Human exposure is common, but infection is rare. Acanthamoeba infection of the CNS occurs almost entirely in immunocompromised or otherwise debilitated patients, but B. mandrillaris may also infect healthy hosts. Sappinia pedata was implicated in one case of amebic encephalitis in Texas.

The life cycle of Acanthamoeba, Balamuthia, and Sappinia involves only 2 stages: cysts and trophozoites (the infective form). The trophozoites form double-walled cysts, which resist eradication. The entry portal is thought to be the skin or lower respiratory tract, with subsequent hematogenous dissemination to the CNS. In infected patients, cysts and trophozoites may be found in tissues.

Symptoms of Granulomatous Amebic Encephalitis

In patients with granulomatous amebic encephalitis, onset is insidious, often with focal neurologic manifestations. Mental status change, seizures, and headache are common.

Acanthamoeba species and B. mandrillaris may also cause skin lesions; patients can present with ulcerative skin lesions and later develop neurologic symptoms and signs. In a few patients with AIDS, disseminated Acanthamoeba infection has affected only the skin.

Survival is uncommon in patients with central nervous system or disseminated disease; death usually occurs between 7 and 120 days after onset.

Diagnosis of Granulomatous Amebic Encephalitis

  • Head CT and/or MRI with contrast

  • Cerebrospinal fluid analysis

  • Biopsy of skin lesions

Diagnosis of granulomatous amebic encephalitis is often postmortem.

Diagnosis of Acanthamoeba infections

In patients with Acanthamoeba infections of the brain, CT with contrast and MRI may show single or multiple space-occupying lesions with ring enhancement, most commonly in the temporal and parietal lobes. In cerebrospinal fluid (CSF), white blood cell (WBC) count (predominantly lymphocytes) is elevated, but trophozoites are rarely seen. These tests help exclude other possible causes but usually cannot confirm the diagnosis.

Visible skin lesions often contain amebas and should be biopsied; if detected, amebas may be cultured and tested for drug sensitivity. Brain biopsy is often positive and should be considered if granulomatous amebic encephalitis is suspected.

Polymerase chain reaction (PCR)–based assays are available in specialized reference laboratories.

Diagnosis of B. mandrillaris infections

In patients with B. mandrillaris infection of the brain, CT and MRI, both with contrast, typically show multiple nodular, ring-enhancing lesions. Intralesional hemorrhage is an important radiologic clue. In CSF the WBC count is elevated (predominantly lymphocytes), the glucose is normal or low, and the protein is often markedly elevated. B. mandrillaris is rarely identified in CSF. Microscopic examination plus PCR-based and immunohistochemical techniques can identify B. mandrillaris in biopsies of brain or skin lesions.

Treatment of Granulomatous Amebic Encephalitis

  • A combination of antiparasitic drugs, including miltefosine

  • Consultation with the Centers for Disease Control and Prevention

Optimal treatment of Acanthamoeba encephalitis is unclear. For all cases, immediate consultation with the Centers for Disease Control and Prevention (CDC) is recommended (call the CDC Emergency Operations Center at 770-488-7100). Multiple drugs (often > 5) are typically used in combination. Although the number of patients treated with a regimen containing miltefosine is small, miltefosine appears to offer a survival advantage and is recommended.

Other drugs that have been used in combination with miltefosine to treat Acanthamoeba encephalitis include pentamidine, sulfadiazine or trimethoprim/sulfamethoxazole, flucytosine, an azole (fluconazole, itraconazole, or voriconazole), rifampin and amphotericin B.

For B. mandrillaris encephalitis, miltefosine in combination with other drugs such as flucytosine, pentamidine, fluconazole, and/or sulfadiazine plus either azithromycin or clarithromycin plus surgical resection have been used.

A case of Sappinia pedata encephalitis was successfully treated with a combination of azithromycin, pentamidine, itraconazole, and flucytosine plus surgical resection of the central nervous system (CNS) lesion. Adding miltefosine to this regimen should be considered in future cases.

Skin and disseminated infections caused by Acanthamoeba species or B. mandrillaris are usually treated with the same drugs plus surgical debridement of cutaneous lesions.

Key Points

  • Granulomatous amebic encephalitis is a very rare, usually fatal, CNS infection.

  • Acanthamoeba encephalitis occurs almost entirely in immunocompromised or otherwise debilitated patients, but B. mandrillaris may infect healthy hosts.

  • Do head CT or MRI, both with contrast; do CSF tests to exclude other causes; biopsy skin lesions, if present, or sometimes the brain to check for amebas.

  • Consult with the CDC about diagnostic testing and optimal treatment.

  • Treat with miltefosine plus other antiparasitic drugs (eg, pentamidine, sulfadiazine, flucytosine, an azole).

More Information

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

Drugs Mentioned In This Article

Drug Name Select Trade
NebuPent, Pentam
No brand name available
Primsol, Proloprim, TRIMPEX
Rifadin, Rifadin IV, Rimactane
Amphocin, Fungizone
Azasite, Zithromax, Zithromax Powder, Zithromax Single-Dose , Zithromax Tri-Pak, Zithromax Z-Pak, Zmax, Zmax Pediatric
Biaxin, Biaxin XL
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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