Granulomatous Amebic Encephalitis in a Child with Acute Lymphoblastic Leukemia Successfully Treated with Multimodal Antimicrobial Therapy and Hyperbaric Oxygen

Abstract

Acanthamoeba is the causative agent of granulomatous amebic encephalitis, a rare and usually fatal disease. We report a child with acute lymphoblastic leukemia who developed brain abscesses caused by Acanthamoeba during induction therapy. Multimodal antimicrobial chemotherapy and hyperbaric oxygen therapy resulted in complete resolution of symptoms and of pathology as seen by magnetic resonance imaging.

CASE REPORT

A 25-month-old boy was treated at our institution for acute lymphoblastic leukemia (ALL). The induction therapy consisted of prednisone, dexamethasone, vincristine, daunorubicin, l-asparaginase, methotrexate, cyclophosphamide, and mercaptopurine. Infection prophylaxis included oral amphotericin B and trimethoprim-sulfamethoxazole (4 mg/kg of body weight/day 4 days/week). Complete remission of ALL was achieved by day 15 of ALL treatment.

Forty-three days after the diagnosis was established and therapy started, the boy developed fever followed by an increase of C-reactive protein (CRP) (maximum, 87.8 mg/liter [normal range, 0 to 8 mg/liter]). Therapy with meropenem and liposomal amphotericin B resulted in defervescence. The patient suffered from mild headache, and 5 days later he experienced left-sided hemiparesis and a second elevation of CRP level (maximum, 37 mg/dl). No other symptoms besides fever and hemiparesis were noted.

Magnetic resonance imaging (MRI) revealed multifocal lesions up to 20 mm in diameter, partially necrotic as seen by increased contrast medium enhancement, and extended edema. The largest lesion was located in the right front parietal lobe. The morphology of these lesions was indicative for abscess formations (Fig. 1).

FIG. 1.

MRI on day 44 of ALL treatment showing multiple abscess formations with diameters of up to 20 mm. Midline shift is 3 to 4 mm.

Analysis of the initially acquired cerebrospinal fluid (CSF) showed 0 erythrocytes/μl, 2 leukocytes/μl, increased protein (62 mg/dl), normal glucose, and no bacteria. An extensive diagnostic workup on fungi, bacteria, and parasites known to cause brain abscesses in children (7) revealed positive PCR results for Acanthamoeba 2 days after the first signs of hemiparesis. An Acanthamoeba-specific PCR amplifying a fragment of the 18S ribosomal DNA (rDNA) was performed using the primers JDP1 and JDP2 (12) and Acanthamoeba strain ATCC PRA-105, genotype T4, as a positive control. For genotyping, amplicons were sequenced using a 310 ABI Prism automated sequencer (Applied Biosystems, Langen, Germany), and the genotype was assessed with the model assumption of a <5% sequence dissimilarity within one genotype (3). Further specification revealed Acanthamoeba group II, genotype T4, known to be the predominant type that causes granulomatous amebic encephalitis (GAE) in humans (13).

Cultures and PCR of the CSF were negative for fungi and bacteria. The results of Acanthamoeba PCR of nasal and respiratory discharge and sputum were negative.

ALL therapy was stopped on treatment day 44, and empirical antimicrobial therapy was initiated, consisting of meropenem, teicoplanin, fosfomycin, metronidazole, and liposomal amphotericin B. Hyperbaric oxygen therapy (HBO) was started empirically for its known effect on brain abscesses as previously described (6, 7), consisting of 36 applications in the pressure chamber once daily at 2.2 atmospheres absolute for 60 min at 12 m within 36 days.

After confirmation of diagnosis 2 days after the first lumbar puncture, treatment was changed to daily trimethoprim-sulfamethoxazole (6 mg/kg/day intravenously [i.v.]), fluconazole (10 mg/kg/day i.v.), pentamidine (4 mg/kg/day i.v. for 20 days), and miltefosine (2.5 mg/kg/day i.v. for 23 days) (13, 15). Additional granulocyte colony-stimulating factor (G-CSF) was given in order to increase the leukocyte count. Phenobarbital was administered as an anticonvulsive prophylaxis.

A repeated lumbar puncture 8 days later still showed positive PCR results for Acanthamoeba DNA and an elevated CSF leukocyte count (293 leukocytes/μl). Three weeks after the initiation of specific therapy, PCR on CSF for Acanthamoeba was negative.

Subsequent MRI studies 14, 30, and 60 days, as well as 90 days, after the first symptoms showed regression of the lesions and edema (Fig. 2).

FIG. 2.

MRI 2 months after diagnosis of brain abscesses showing further regression. Maximum diameter of lesions is 11 mm.

The treatment was very well tolerated, with only mild laboratory signs of pancreatitis. ALL polychemotherapy was resumed after 12 days. To date, the patient has completed maintenance therapy and has been in complete remission for 22 months. He achieved complete resolution of neurologic symptoms after 4 months.

Acanthamoeba is a free-living amoeba distributed worldwide in soil, fresh and brackish water, dust, hot tubs, and sewage (2). Most people seem to have been exposed to this organism during their lifetime, since most healthy individuals show serum antibodies against Acanthamoeba (8). Acanthamoeba causes three distinct clinical syndromes. One is Acanthamoeba keratitis following minor corneal trauma in immunocompetent patients, usually appearing in contact lens wearers. Another is disseminated Acanthamoeba infections involving skin, sinuses, and lungs that typically occur in immunocompromised patients, including those with AIDS, systemic lupus erythematosus, steroid use, malnutrition, or liver disease and transplant recipients and patients receiving chemotherapy. And the third is GAE, usually affecting immunocompromised patients.

Acanthamoeba may enter through skin lesions or the respiratory tract and spread hematogenously to the central nervous system (CNS). The route of infection in our patient was not clear. The child lives in a rural region; however, analysis of drinking water was negative for Acanthamoeba.

Two other amebic genera are known to cause CNS infections, Naegleria fowleri and Balamuthia mandrillaris. While infections with Balamuthia mandrillaris are clinically very similar to infections with Acanthamoeba, Naegleria fowleri causes primary amebic meningoencephalitis, usually in immunocompetent individuals and children. Treatment is based on the administration of amphotericin B in combination with other drugs (9, 14), but results are generally poor. GAE in immunocompetent persons is extremely rare (16).

The symptoms of GAE are generally nonspecific and include headache (53%), meningismus (40%), fever (53%), mental status changes (86%), visual disturbances (26%), ataxia (20%), hemiparesis (53%), and seizures (66%). The exact incubation period is unknown but is probably weeks to months. The duration of disease is reported to range from 7 to 120 days (average, 39 days). The clinical course of GAE is often fatal (5).

Diagnosis of GAE is based on CSF analysis, including microscopic examination, culture, and PCR (11). PCR is especially useful in cases with low parasite density (16). Acanthamoeba amebas grow in culture on nonnutritive agar overlaid with Gram-negative bacteria. If a culture is positive, susceptibility testing should be done (1). Acanthamoeba amebas are sensitive to multiple antimicrobial agents (13).

Ofori-Kwakye et al. reported on a 7-year-old girl with GAE who was treated successfully; after surgical intervention and treatment with ketoconazole, her neurological symptoms slowly resolved (10). A 17-year-old patient with ALL and amebic encephalitis was treated successfully with ketoconazole (5 mg/kg/day), trimethoprim-sulfamethoxazole (15 mg/kg/day), and rifampin (10 mg/kg/day). Diagnosis of Acanthamoeba infection was confirmed by positive CSF culture. Nevertheless, the patient died in consequence of the preexisting ALL (4). Another case of GAE occurring in a patient following liver transplantation was reported in 2008 by Fung et al. Surgical intervention was performed, as well as multimodal chemotherapy. Final diagnosis was established microscopically in a lobectomy specimen. Rifampin (600 mg twice a day) and co-trimoxazole (960 mg twice a day) were added as specific therapy after the identification of Acanthamoeba. The patient survived with massive neurological residuals (2).

In the case reported here, we initially instituted empirical therapy with meropenem, teicoplanin, and amphotericin B and added therapy with pentamidine, fluconazole, metronidazole, trimethoprim-sulfamethoxazole, and miltefosine when infection with Acanthamoeba was established (13).

Since recovery on only antimicrobial therapy is rare and surgical intervention was not possible due to the location of the abscess formations, we started additional hyperbaric oxygen therapy, a treatment modality recently described for patients with brain abscesses (6, 7).

To the best of our knowledge, this is the first case of GAE in childhood occurring during treatment of ALL in which diagnosis was confirmed by CSF-PCR and with full recovery without any neurological deficits. Because there is no therapeutic guideline yet, antimicrobial therapy must be wide and aggressive. Single cerebral lesions should be excised if possible, and especially if they are not surgically excisable, hyperbaric oxygen therapy might be an additional treatment option.

Nucleotide sequence accession number.

Sequence data for the Acanthamoeba group II, genotype T4 strain found in this study have been deposited in GenBank under accession number HQ450394.