There are three main pathologic free-living Amebas (not including the gastrointestinal parasite
Entamoeba histolytica) which are as follows:
Naegleria fowleri,
Acanthamoeba species, and
Balamuthia mandrillaris.[
14]
Naegleria are associated with primary amebic meningoencephalitis, a rapidly fatal hemorrhagic encephalitis typically occurring in healthy children or young adults and usually following recent fresh water swimming.
Acanthamoeba and
Balamuthia both can cause the syndrome of GAE, which our patient had, an insidious and almost uniformly fatal encephalitic process.[
5,
6]
Acanthamoeba is also associated with keratitis in otherwise healthy individuals, typically contact lens wearers who use homemade solutions to clean lenses or wear lenses while swimming in fresh water, and with chronic skin ulcers.[
5,
6]
Acanthamoeba are found worldwide in a variety of habitats, including freshwater, soil, air, and sewage.[
2] They have also been isolated from the nasopharyngeal passages of healthy persons and may be considered normal flora.[
16] Serologic surveys have detected serum antibodies against
Acanthamoeba in healthy individuals.[
2]
Despite the ubiquitous nature of the organism and common exposure, the incidence of human disease from
Acanthamoeba is low. GAE from
Acanthamoeba occurs almost exclusively in immunocompromised hosts or debilitated patients. HIV disease, systemic lupus erythematosus, diabetes, chronic liver disease, chemotherapy, prolonged steroid, and organ and marrow transplantation have all been described as potential associations.[
2,
4,
6–
9,
16]
Acanthamoeba encephalitis has also been reported in immunocompetent hosts, although much less commonly.[
17] Recently, a case of
Acanthamoeba encephalitis was reported in a patient who received rituximab for cryoglobulinemia.[
10] The patient also received plasmapheresis, but steroids were being tapered at the time of disease occurrence. Our patient had an ill-defined chronic liver disease with no cirrhosis on biopsy, was on a low and tapering dose of steroids for a short period of time, and was taking 6-MP.
The portal of entry of cases of Naegleria meningoencephalitis is usually through the olfactory neuroepithelium. Although Acanthamoeba more commonly gain access to the CNS hematogenously either through the respiratory tract or skin, organisms can also enter through the olfactory route. The frontal location of the infection in our patient suggests an olfactory site of entry. However, our patient demonstrated ecchymotic skin lesions, one or more of which could have represented a site of entry.
The diagnosis in our patient was not certain until brain biopsy was performed as is typical. It is possible that if the diagnosis had been considered and the treatment initiated sooner, the patient could have had a better outcome. The febrile nature of the illness was a clue to the diagnosis, but this was not considered because of the unusual imaging and the intercurrent gastrointestinal illness. The immunosuppression, though considered “mild,” could also have alerted the medical team to the presence of an unusual or opportunistic infection. The initial imaging, which demonstrated no enhancement on MRI, suggested relatively benign entities, such as low-grade glioma and tumefactive demyelination, rather than an inflammatory process. However, in GAE, enhancement may or may not be seen on imaging studies despite the presence of an aggressive necrotizing parasitic infection.[
11–
13]
Although GAE is not new to the international medical literature, it is nonetheless exceptionally rare.
Treatment options for GAE are not well-defined as the majority of cases are diagnosed postmortem. Although our patient did not improve with aggressive surgical and medical treatment, there have been reports of successful treatment.[
1,
3,
4,
9,
14,
17] Despite many anecdotal antimicrobial regimens in the literature, no regimen is universally accepted or effective.
