Encephalitis Due to a Free-Living
Amoeba (Balamuthia mandrillaris):
Case Report with Literature Review
Inderjit Deol, M.D.,* Laura Robledo, M.D.,† Armando Meza, M.D.,‡
Govinda S. Visvesvara, Ph.D.,¶ and Russell J. Andrews, M.D.§
*Department of Pathology, †Department of Surgery, ‡Department of Internal Medicine, and
§Division of Neurosurgery, Texas Tech University Health Sciences Center, El Paso, Texas,
¶Division of Parasitic Diseases, Centers for Disease Control and Prevention, Atlanta,
Georgia

Encephalitis due to a free-living amoeba (Balamuthia mandrillaris): case report with literature review. Surg Neurol
2000;53:611– 6.
BACKGROUND

Amebic infections can spread to the central nervous system with a lengthy but usually fatal course. A typical case
is presented to raise awareness of this increasingly reported infectious process that may have a more favorable
outcome if diagnosed in its early stages.
CASE DESCRIPTION

A 38-year-old male presented with an ulcerating 10 ⫻ 8
cm mass on his thigh and smaller skin nodules. In less
than 6 months seizures developed due to granulomatous
lesions of the brain. Biopsies/excisions of the thigh lesion, a subcutaneous nodule, and a brain lesion were
performed. He failed to respond to broad spectrum antibiotics and antineoplastic agents, and died within 6
weeks of the initial MRI scan of the brain.
Rare amebic trophozoites were appreciated in the biopsy specimens on post-mortem review, and Balamuthia
mandrillaris confirmed as the infecting agent on immunofluorescence studies.
CONCLUSIONS

Granulomatous amebic encephalitis is a parasitic infection with a lengthy clinical course before rapid deterioration due to extensive brain lesions is noted. Either early
treatment with antimicrobials or—in rare cases—
excision of the brain lesion(s) may offer the chance of a
cure. © 2000 by Elsevier Science Inc.
KEY WORDS

Amebiasis, encephalitis, granulomatous infection (chronic),
parasites.

mebic infections of the central nervous system (CNS) have been recognized for over 30
years, but increasingly over the last 10 years re-

A

Address reprint requests to: Dr Russell J. Andrews, Division of Neurosurgery, Texas Tech Health Sciences Center, 4800 Alberta Avenue, El Paso,
TX 79905.
Received September 23, 1999; accepted April 6, 2000.
© 2000 by Elsevier Science Inc.
655 Avenue of the Americas, New York, NY 10010

ports have appeared documenting the various
types of amebic infections and their usually fatal
outcome. Primary amebic meningoencephalitis
(PAM), which is usually fatal within 1 week of onset,
usually requires neurosurgical intervention only if
hydrocephalus develops. Granulomatous amebic
encephalitis (GAE) has a much more prolonged
course, is characterized by mass lesions of the
CNS in its terminal stages, and unfortunately has
an even more uniformly fatal outcome. The following case is presented because 1) amebic infections of the CNS are likely more common than
is appreciated, and 2) the pathological diagnosis
can be elusive.

Case Report
On July 20, 1998, a 38-year-old Hispanic male presented with a history of a subcutaneous mass on his
right thigh that had slowly enlarged for over 1 year.
Additional, much smaller subcutaneous masses of
the face and neck had also been present for over 1
year. The thigh mass was initially less than 1 cm in
diameter, but had doubled in size over 6 months.
The thigh mass increased more dramatically over
the following 6 months, with ecchymosis and central ulceration occurring over the last month. He
also had a 5 kg weight loss. Although the patient
had a history of prostitute and homosexual contacts, as well as intravenous cocaine use as recently
as 2 months previously, testing for syphilis and HIV
were negative.
On examination, the patient had a 10 ⫻ 8 cm firm,
nontender, mobile mass on the mid lateral right
thigh, with a one cm central ulceration. He underwent CT and MRI scans of the right thigh, and an
0090-3019/00/$–see front matter
PII S0090-3019(00)00232-9

612 Surg Neurol
2000;53:611–6

incisional biopsy. The pathological findings of this
procedure, and the several which followed, are discussed below.
On October 5, 1998, the patient was readmitted
for an excisional biopsy after the incisional biopsy
failed to reveal an etiology. Repeated attempts at
skin grafting were unsuccessful due to recurrent
infections.
On December 27, 1998, the patient was admitted
for evaluation of multiple painless subcutaneous
masses, as well as for seizures. He had had three
tonic-clonic seizures over the preceding two
months and had been started on phenytoin. On
examination, the patient had 3 ⫻ 3 cm mass in the
left maxillary area and a 1 ⫻ 1 cm mass on the back
of his neck. Both were hard, indurated, and nontender. Both CT and MRI scans of the brain showed
two contrast-enhancing lesions: a 1 cm mass in the
right temporal lobe and a 3 cm mass in the right
occipital lobe (Figure 1). Repeat HIV testing during
this admission was again negative. A fine needle
aspirate of the posterior neck mass was performed,
followed by an incisional biopsy the next day (results presented below).
The lack of tissue diagnosis prompted a stereotactic brain biopsy of the right occipital lesion—
followed immediately by excision under intravenous sedation because the frozen section was
nondiagnostic— on January 5, 1999. The tissue in
the region of the lesion was adherent to the dura,
quite firm, and without a discrete capsule. A 3 cm
cavity resulted from removing the clearly abnormal
tissue. He was discharged January 9 on phenytoin
and prednisone.
On January 20, the patient presented with headaches, continued seizures, and lethargy. On physical examination, the masses on the neck and maxillary area were unchanged. Anisocoria was noted
with the left pupil measuring 2 mm and the right
four mm, and a mild left hemiparesis was present.
An MRI scan done on January 25 showed more
than 10 contrast-enhancing lesions involving both
hemispheres, the diencephalon, cerebellum, and
brain stem (Figure 2). The patient was treated with
broad spectrum antibiotics. Because of the lack
of a diagnosis and the suspicion of neoplasia,
chemotherapy was discussed with the patient’s
family. Cytoxan was administered on January 28
with no response. The patient deteriorated rapidly, from a Glasgow Coma Scale (GCS) 13 to GCS
3, in less than a week. The patient died on February 8 of cardiorespiratory arrest. An autopsy was
performed.

Deol et al

Contrast-enhanced T-1 weighted MR images of the
brain (December 29, 1998). (A) A one cm lesion is
present in the right temporal lobe. (B) A three cm lesion
is present in the right occipital lobe.

1

Pathology
The needle aspiration and incisional biopsies of the
thigh and neck subcutaneous masses showed
marked necrotizing granulomatous chronic inflammatory reaction with angiitis. The thigh specimen
underwent special stains for fungi and acid fast
bacteria (Gomori’s Methenamine Silver and Acid
Fast Bacilli), and cultures (including mycobacteria)
that grew Pseudomonas spp. and Porphyromonas
spp. The brain biopsy showed no granuloma forma-

Granulomatous Amebic Encephalitis

Surg Neurol 613
2000;53:611–6

sections revealed multiple areas of hemorrhagic
necrosis throughout the cerebrum, diencephalon,
brainstem, and cerebellum. The microscopic findings included hemorrhagic necrosis, chronic inflammation, and vasculitis. Both the biopsy and
autopsy specimens from the brain were sent to the
Armed Forces Institute of Pathology (AFIP) for
review.
Because of the lack of a tissue diagnosis, the
biopsy and autopsy specimens were again reviewed. Rare degenerating amebic trophozoites
were seen in the biopsy materials of the skin and
brain lesions, as well as more numerous amebic
trophozoites and cysts in the brain autopsy specimens, predominantly in the perivascular spaces
(Figure 3). The amebae were lying free within the
brain parenchyma as well as in the necrotic areas.
The material was reviewed again by neuropathologists at the AFIP, who confirmed the diagnosis of
GAE.
Immunofluorescence studies performed by Dr. G.
Visvesvara [26] demonstrated that these amebae
reacted with an antiserum against Balamuthia but not
with antiserum against Naegleria and Acanthamoebae.

Discussion

Contrast-enhanced T-1 weighted MR images of the
brain (January 25, 1999). (A) The right occipital
lesion has recurred and is much larger, and new left
caudate and temporal lobe lesions are seen. (B) A coronal
view shows multiple lesions in the right hemisphere, left
cerebellum, midbrain, and brainstem.

2

tion, but did show severe necrotizing chronic inflammation with angiitis and thrombosis. Special
stains again were negative for fungus and mycobacteria, as they were for the neck biopsy. Culture for
microorganisms was negative. The differential diagnoses considered were infectious process, sarcoidosis, and lymphomatoid granulomatosis.
At autopsy, the cerebral hemispheres were edematous with softening of the cortical surface. Cut

The free-living amebae producing CNS lesions in humans include Naegleria fowleri, Acanthamoeba species and Balamuthia mandrillaris. N. fowleri produces
primary amebic meningoencephalitis (PAM), which
has an abrupt onset and rapid progression to coma
and death [4,11,14,15,23]. Usually PAM occurs in
healthy individuals with a recent history of waterrelated activities. Acanthamoeba can cause a keratitis
for which effective treatment is lacking, with over 750
cases reported worldwide as of 1996 [4,11,14,15].
Acanthamoeba and Balamuthia can cause GAE, which
has a subacute to chronic course and an almost invariably fatal outcome [4,11,12,14,15,23,25].
Acanthamoeba and Balamuthia species have a
ubiquitous distribution, with organisms found in
soil, water, and heating and air-conditioning units
[15]. Cases of GAE due to these pathogens have
been reported from Argentina (24), Austria (14),
Brazil (2), Canada (14), Czechoslovakia (10), Italy
(3), Mexico (18), Nigeria (14), Peru (14), United
States (9), and Venezuela (6). GAE can occur in any
age group, with a M:F ratio of 5:1. GAE can be seen
in healthy patients, as well as in immunosuppressed patients such as those with AIDS (Table 1)
[7,11,17,18,27]. Predisposing factors and underlying
diseases may play a role in the development of GAE.
Although the route of invasion and penetration into

614 Surg Neurol
2000;53:611–6

Deol et al

Photomicrograph of the
brain lesion. There is a vessel centrally with perivascular
amebic trophozoites and a cyst.
The trophozoites are irregularly
shaped with abundant cytoplasm containing vacuoles and
granular material. In the top center is a round amebic cyst with a
characteristic
double
wall
(H&E ⫻ 100).

3

the brain in GAE is still unknown, hematogenous
spread has been postulated with a possible primary
entry via the skin or respiratory tract.
GAE is no doubt underrecognized at present. Although as of 1989 less than 50 cases of GAE had
been reported worldwide [11], by late 1996 the
number of cases reported had risen to nearly 200
[13, 14]. Of these, only three have been documented
survivors, all of whom had Acanthamoeba infections [14,15]. Many patients with GAE presented
with dermal lesions of varying duration, from 2
months to 3 years [17]. The first report of Balamuthia being cultured from human tissue specimens was in 1992, from a patient presenting with a
rapidly enlarging thigh lesion similar to the present
case [7].
This case showed the characteristic neuropathologic findings of GAE, i.e., necrotizing encephalitis
with trophozoites and cysts produced by Balamuthia [13]. The patient initially presented with
skin and subcutaneous lesions, and subsequently

1

died of CNS involvement. The route of entry was
presumably skin in this case, as other organs (notably the lung) were not involved. Dissemination to
the CNS was probably by the hematogenous route.
Despite risk factors such as i.v. drug abuse and
prostitute exposure, the patient was HIV negative
on two occasions. Serum immunoglobulin level and
B and T-cell marker studies were not performed.
The brain lesions of GAE may or may not show
granuloma formation. The lack of granuloma formation in the brain lesions in the present case could be
due to prolonged immunosuppressive therapy or
other immunodeficiency status. Systemic dissemination of B. mandrillaris has been seen only in one
immunocompromised patient with acquired immunodeficiency syndrome in whom trophozoites were
found at autopsy in the kidneys and adrenal glands
[1,18]. No other organ outside the brain and skin
was found to be affected in this case.
The diagnosis of GAE in life requires a high degree of suspicion; thus most cases have been iden-

Comparison of Clinical, Pathological Features and Prognosis of Granulomatous Amebic Encephalitis (GAE), and
Primary Amebic Meningoencephalitis (PAM)

FEATURES
Etiologic agent
Predisposing factors
Portal of entry
Clinical course
Prognosis
Histopathology

GAE
Acanthamoebae species Balamuthia
mandrillaris
Chronic debilitating diseases,
immunodeficiency conditions
Respiratory tract, skin
Subacute or chronic
Very poor (usually fatal)
Cysts and trophozoites, often perivascular,
hemorrhagic necrosis, vasculitis,
inflammation with or without granuloma
formation

PAM
Naegleria fowleri
Healthy individuals, exposure to
contaminated fresh water
Nasal epithelium
Acute (death within days)
Very poor (usually fatal)
Trophozoites only, often perivascular,
hemorrhagic necrosis and inflammation

Granulomatous Amebic Encephalitis

tified retrospectively post-mortem. Rare degenerating amebic forms in the skin lesions were identified
in the present case retrospectively, in both the
brain biopsy and the brain autopsy specimens.
No characteristic clinical symptoms, laboratory,
and radiologic findings have been found to be diagnostic of GAE. CT or MRI neuroimaging usually
shows one or more contrast-enhancing lesions
which are nonspecific, and could be seen in conditions such as bacterial and fungal infections, tuberculomas, toxoplasmosis, or neoplasm [5,9,19,22].
A brain biopsy is important for making the diagnosis of GAE, and may be part of curative treatment
if the process has not evolved to diffuse encephalitis. One case has been reported of a seven-year-old
girl with a single Acanthamoeba-induced granuloma
in the parietal lobe who was cured (i.e., disease-free
at 1 year) by excision followed with ketoconazole
therapy for 8 months [16]. Usually, however, GAE
presents with multiple lesions in areas throughout
the brain that precludes surgical excision of the
lesion(s) as a therapeutic option.
This one case notwithstanding, in light of the
usually fatal prognosis after CNS involvement, early
diagnosis of the skin lesion(s) that may be a sign of
impending CNS infection could allow for early diagnosis and treatment. Unfortunately, an antiparasitic
agent that is both efficacious and without significant
side effects has yet to be recognized. Some in vitro
studies show that pentamidine, azithromycin, and
certain phenothiazines can inhibit the growth of
Balamuthia, but none are amebicidal at non-toxic
concentrations [20,21]. With the development of a
murine model of GAE, however, a method now exists for rapid evaluation of potential therapeutic
protocols to treat GAE—with the hope that a truly
efficacious treatment for this relatively rare but
deadly disease might be found [8].
If clinicians and surgical pathologists are aware of
GAE, the diagnosis can be readily made because
amebic trophozoites and cysts have characteristic
morphology under light microscopy. It is possible
at that stage that curative treatment with antiparasitic agent(s) (or other agents, as discussed in the
previous paragraph) might be instituted. For cases
presenting with brain involvement, excision of the
lesions noted on contrast CT (or preferably MRI)
scan followed by prolonged treatment with antiparasitic agents might also be curative. The present
case illustrates that the presence of free-living amebae should be considered in the differential diagnosis of inflammatory nodular subcutaneous lesions
that can subsequently involve the CNS—with the
dismal prognosis that GAE currently holds.

Surg Neurol 615
2000;53:611–6

We thank Kay Nippes, R.N., for gathering much of the clinical information and literature reviewed in this paper.

REFERENCES
1. Anzil AP, Rao C, Wrzolek MA, Visvesvara GS, Sher JH,
Kozlowski PB. Amebic meningoencephalitis in a patient with AIDS caused by a newly recognized opportunistic pathogen: Leptomyxid ameba. Arch Pathol
Lab Med 1991;115:21–5.
2. Chimelli L, Hahn MD, Scaravilli F, Wallace S, Visvesvara GS. Granulomatous amoebic encephalitis due to
Leptomyxid amoeba: Report of the first Brazilian case.
Transact Roy Soc Trop Med Hyg 1992;86:635.
3. Di Gregorio C, Rivasi F, Mongiardo N, De Rienzo B,
Wallace S, Visvesvara GS. Acanthamoeba meningoencephalitis in a patient with acquired immunodeficiency syndrome. Arch Pathol Lab Med 1992;116:
1363–5.
4. Durack DT. Amebic infections. In Scheld WM, Whitley
RJ, Durack DT, eds. Infections of the Central Nervous
System, 2nd ed. Philadelphia: Lippincott–Raven,
1997:831– 44.
5. Falcon S, Quencer RM, Post MJD. Magnetic resonance
imaging of unusual intracranial infections. Topics in
Mag Reson Imaging 1994;6:41–51.
6. Gonzalez–Alfonzo JE, Martinez AJ, Garcia V, Garcia–
Tamayo J, Cespedes G. Granulomatous encephalitis
due to Leptomyxid amoeba: Short report. Transact
Roy Soc Trop Med Hyg 1991;85:480.
7. Gordon SM, Steinberg JP, DuPuis MH, Kozarsky PE,
Nickerson JF, Visvesvara GS. Culture isolation of
Acanthamoeba species and Leptomyxid amebas from
patients with amebic meningoencephalitis, including
two patients with AIDS: Review article. Clin Infect Dis
1992;15:1024 –1030.
8. Janitschke K, Martinez AJ, Visvesvara GS, Schuster F.
Animal model Balamuthia mandrillaris CNS infestion:
Contrast and comparison in immunodeficient and immunocompetent mice: A murine model of “granulomatous” amebic encephalitis. J Neuropathol Exp Neurol 1996;55:815– 821.
9. Kidney DD, Kim SH. CNS infections with free-living
amebas: Neuroimaging findings. AJR 1998;171:809 –12.
10. Kodet R, Nohynkova E, Tichy M, Soukup J, Visvesvara
GS. Amebic encephalitis caused by Balamuthia mandrillaris in a Czech child: Description of the first case
from Europe. Pathol Res Pract 1998;194:423–30.
11. Ma P, Visvesvara GS, Martinez AJ, Theodore FH, Daggett P-M, Sawyer TK. Naegleria and Acanthamoeba
infections: Review. Rev Infect Dis 1990;12:490 –513.
12. Martinez AJ, Janitschke K. Acanthamoeba, an opportunistic microorganism: A review. Infection 1985;13:
251–256.
13. Martinez AJ, Visvesvara GS. Laboratory diagnosis of
pathogenic free-living amoebas: Naegleria, Acanthamoeba, and Leptomyxid. Clin Lab Med 1991;11:861–
872.
14. Martinez AJ, Visvesvara GS. Free-living, amphizoic,
and opportunistic amebas. Brain Pathol 1997;7:583–
98.
15. Martinez AJ, Visvesvara GS, Chandler FW. Free-living
amebic infections. In Connor DH, Chandler FW,
Schwartz DA, Manz HJ, Lack EE, eds. Pathology of

616 Surg Neurol
2000;53:611–6

Infectious Diseases, Vol. II. Stamford CT: Appleton &
Lange, 1997:1163–76.
16. Ofori–Kwakye SK, Sidebottom DG, Herbert J, Fischer
EG, Visvesvara GS. Granulomatous brain tumor
caused by Acanthamoeba: Case report. J Neurosurg
1986;64:505–509.
17. Recavarren–Arce S, Velarde C, Gotuzzo E, Cabrera
J. Amoeba angeitic lesions of the central nervous
system in Balamuthia mandrilaris amoebiasis. Hum
Pathol 1999;30:269 –273.
18. Riestra–Castaneda
JM,
Riestra–Castaneda
R,
Gonzalez–Garrido AA, Moreno PP, Martinez AJ, Visvesvara GS, Careaga FJ, Oropeza de Alba JL, Cornejo
SG. Granulomatous amebic encephalitis due to Balamuthia mandrillaris (Leptomyxidae): Report of four
cases from Mexico. Am J Trop Med Hyg 1997;56:603–
607.
19. Schumacher DJ, Tien RD, Lane K. Neuroimaging findings in rare amebic infections of the central nervous
system. AJNR 1995;16:930 –935.
20. Schuster FL, Visvesvara GS. Axenic growth and drug
sensitivity studies of Balamuthia mandrillaris, and
agent of amebic meningoencephalitis in humans and
other animals. J Clin Microbiol 1996;34:385–388.
21. Schuster FL, Visvesvara GS. Efficacy of novel antimicrobials against clinical isolates of opportunistic
amebas. J Euk Microbiol 1998;45:612– 618.
22. Sell JJ, Rupp FW, Orrison WW. Granulomatous amebic encephalitis caused by Acanthamoeba. Diagnostic
Neuroradiology 1997;39:434 – 6.
23. Simon MW, Wilson HD. The amebic meningoencephalitides. Pediatr Infect Dis 1986;5:562–9.
24. Taratuto AL, Monges J, Acefe JC, Meli F, Paredes A,
Martinez AJ. Leptomyxid amoeba encephalitis: Report
of the first case in Argentina. Transact Roy Soc Trop
Med Hyg 1991;85:77.
25. Visvesvara GS, Martinez AJ, Schuster FL, Leitch GJ,
Wallace SV, Sawyer TK, Anderson M. Leptomyxid
ameba, a new agent of amebic meningoencephalitis in
humans and animals. J Clin Microbiol 1990;28:2750 – 6.
26. Visvesvara GS, Schuster FL, Martinez AJ. Balamuthia
mandrillaris, N. G., N. sp., agent of amebic meningoencephalitis in humans and other animals. J Euk Microbiol 1993;40:504 –14.
27. Zagardo MT, Castellani RJ, Zoarski GH, Bauserman

Deol et al

SC. Granulomatous amebic encephalitis caused by
Leptomyxid amebae in an HIV-infected patient. AJNR
1997;18:903– 8.

COMMENTARY

Fewer than 80 human cases of granulomatous amebic encephalitis due to Balamuthia have been reported; in all cases, the patient died. As shown in
the study by Deol et al, an early diagnosis is not
usually made because a search for the free-living
amoeba is not specifically directed. This is most
unfortunate because in many cases, the systemic
infection runs a chronic course, showing typical
skin lesions long before the neurological disorder
begins its fatal course. The fact that in most of the
reports the agent was not suspected and the diagnosis was only made at autopsy means that there
have been very few attempts at treatment. Recently,
some drugs have shown reasonable effectiveness in
experimental studies—particularly pentamidine
and phenothiazines— however, their dose and clinical efficacy still await human trials. Again, diagnostic difficulties preclude such studies.
This case reminds us that in chronic infectious
diseases of obscure origin every effort should be
made to find the offending agent. In this case a brain
biopsy was performed, but the amoeba was discovered only on review after the death of the patient.
Two main points can be derived from this report:
any granulomatous chronic disorder of skin and
brain could be due to a free-living amoeba, and
effective treatments for these infections remain to
be found.
Julio Sotelo, M.D.
Instituto Nacional de Neurologia y Neurocirurgia
Manuel Velasco Suarez
Mexico City, Mexico