Granulomatous amebic encephalitis is a very rare, usually fatal infection of the brain caused by the free-living amebas Acanthamoeba species, Balamuthia mandrillaris, and Sappinia pedata. It usually occurs in people with a weakened immune system or generally poor health.
The amebas probably enter through the skin or lungs and spread to the brain through the bloodstream.
Symptoms begin gradually and include confusion, headache, blurred vision, seizures, and skin sores.
Imaging tests of the brain and a spinal tap can help doctors exclude other potential causes. A sample of a skin sore or sometimes of brain tissue is taken and examined under a microscope to look for amebas.
Doctors typically use a combination of medications including miltefosine to treat the infection.Doctors typically use a combination of medications including miltefosine to treat the infection.
Free-living amebas are protozoa, which is a type of parasite. They make up a diverse group of microscopic, one-celled organisms. Although they rarely cause infections in people, certain types of these amebas can cause serious, life-threatening infections.
The free-living amebas Acanthamoeba, Balamuthia mandrillaris, and Sappinia pedata are further categorized as extraintestinal protozoa (see also Introduction to Extraintestinal Protozoa), which means they cause infections only in areas outside of the intestines such as the skin and brain.
Acanthamoeba species, Sappinia species, and Balamuthia mandrillaris are present worldwide in water, dust, and/or soil. Many people are exposed to these amebas, but few becomes infected. Infection usually occurs in people whose immune system is weakened or whose general health is poor, but Balamuthia mandrillaris may infect healthy people too.
These amebas do not need a human or animal host to live, but they can enter a body through the skin or lungs and spread to the brain through the bloodstream.
Granulomatous amebic encephalitis differs from primary amebic meningoencephalitis. Primary amebic meningoencephalitis, though also rare, can affect healthy people who swim in fresh water. Primary amebic meningoencephalitis is caused by a free-living ameba called Naegleria fowleri, which is thought to enter the central nervous system through the nose.
(See also Overview of Parasitic Infections.)
Symptoms of Granulomatous Amebic Encephalitis
Symptoms of granulomatous amebic encephalitis begin gradually. Confusion, headache, and seizures are common and occur over weeks to months. People may have a low fever, blurred vision, changes in personality, and problems with speaking or coordination. One side of the body or face may become gradually paralyzed over time.
Acanthamoeba species and Balamuthia mandrillaris may cause skin sores in addition to the symptoms above. In a few people who have advanced HIV infection (also called AIDS), infection caused by Acanthamoeba affects only the skin.
Even with treatment, the symptoms progress to delirium and coma. Granulomatous amebic encephalitis is ultimately fatal, usually 7 to 120 days after symptoms begin.
Diagnosis of Granulomatous Amebic Encephalitis
Imaging tests of the brain
A spinal tap and analysis of cerebrospinal fluid
Biopsy of skin sores and sometimes of brain tissue
Polymerase chain reaction (PCR) testing to check for the genetic material of the ameba
Doctors do various tests to determine which ameba is causing the infection.
Imaging tests of the brain, such as Computed tomography (CT) and magnetic resonance imaging (MRI), are usually done to look for lesions caused by the amebas. Doctors also do a spinal tap (lumbar puncture) to obtain a sample of cerebrospinal fluid (the fluid that surrounds the brain and spinal cord) for testing. These tests help doctors exclude other possible causes of the infection.
Skin sores typically contain amebas. If sores are present, doctors remove samples and examine them under a microscope (biopsy). Doctors may also biopsy brain tissue.
Doctors also do PCR tests on a brain tissue sample to look for the genetic material (DNA) of the ameba.
Granulomatous amebic encephalitis is often diagnosed only after death.
Treatment of Granulomatous Amebic Encephalitis
A combination of medications
Doctors use a combination of medications to treat people who have granulomatous amebic encephalitis. They change which medications are given depending on which ameba is causing the infection.
The medication miltefosine is given to all people who have granulomatous amebic encephalitis regardless of which ameba is the cause. Miltefosine is given in combination with 1 or more of the following medications: is given to all people who have granulomatous amebic encephalitis regardless of which ameba is the cause. Miltefosine is given in combination with 1 or more of the following medications:
PentamidinePentamidine
Sulfadiazine or trimethoprim/sulfamethoxazoleSulfadiazine or trimethoprim/sulfamethoxazole
FlucytosineFlucytosine
Fluconazole, voriconazole, or itraconazoleFluconazole, voriconazole, or itraconazole
ItraconazoleItraconazole
Amphotericin BAmphotericin B
Azithromycin or clarithromycinAzithromycin or clarithromycin
RifampinRifampin
CaspofunginCaspofungin
Some of these medications are taken by mouth, and others are given by injection. Some can be given in more than one way.
Although miltefosine can cause birth defects in a fetus, doctors may give it to infected pregnant people anyway because granulomatous amebic encephalitis is usually fatal without treatment, so the potential benefits of therapy outweigh the risks to the fetus. Women of childbearing age who are taking this medication must use effective birth control measures.
Sometimes surgery is also needed. Surgical removal of the affected tissue can quickly reduce pressure inside the skull and helps doctors confirm the diagnosis through laboratory tests.
Skin sores, if present, are cleaned.
More Information
The following English-language resource may be useful. Please note that The Manual is not responsible for the content of this resource.
Centers for Disease Control and Prevention (CDC): About Acanthamoeba Infections
Drugs Mentioned In This Article
