Fatal Balamuthia Amebic Encephalitis in a Healthy Child: A Case Report with Review of Survival Cases
A previously healthy 4-year-old Thai female patient initially presented with 1-month history of subacute intermittent bi-temporal headache with projectile vomiting, in the absence of fever or diarrhea. Two weeks later, she developed unstable gait to the right side, and loss of distance approximation. There was no history of major illnesses, including sinusitis, pneumonia, chronic skin lesion, or any history of swimming in fresh water. She lived in Buriram province, the northeastern part of Thailand in rural settings, exposed to soil.\nPhysical examinations revealed an afebrile child with no meningeal signs. Her mental status was appropriate for her age. Abnormal neurological signs were head tilt to the right, jerky pursuit with nystagmus, hypometric succade, wide-based gait, and dysdiadochokinesia, which indicated right cerebellar hemispheric lesion. Computer tomography (CT) scan of the brain at a local hospital showed an ill-defined 4.4 cm isodensity mass without calcification in the posterior fossa displaying heterogeneous enhancement on post-contrast study and obstructive hydrocephalus. A referral was made with the diagnosis of a cerebellar tumor.\nMagnetic resonance imaging (MRI) of the brain at King Chulalongkorn Memorial Hospital () showed a 3.0×4.1×2.5 cm ill-defined infiltrating heterogeneously enhanced mass mainly occupying the right inferior cerebellar hemisphere with perilesional edema, causing right tonsillar herniation and mild obstructive hydrocephalus, highly suspicious for a malignant tumor such as medulloblastoma or high-grade glioma. Infectious cause, however, could not be excluded. Total excision of the mass was performed on day 7, and intraoperative finding revealed an infiltrative mass at the right cerebellum involving the hemisphere and tonsil with yellowish plaque and small cystic degeneration. The lesion was completely removed without any residual tumor detected by postoperative ultrasonography. The specimen was fixed in 10% neutral formalin, routinely processed, and embedded in paraffin wax. Pathological examination demonstrated severely inflamed cerebellar tissue, with presence of scattered amebic trophozoites (). The organisms tended to aggregate around blood vessels. No cyst form was observed. Dense lymphocyte infiltrates, aggregates of foamy histiocytes, few vague granulomata, and foci of tissue necrosis were found. The pathological diagnosis of amebic meningoencephalitis led to a prompt start of combined therapy of pentamidine (4 mg/kg/day), sulfasalazine (200 mg/kg/day), fluconazole (12 mg/kg/day), clarithromycin (14 mg/kg/day), and amphotericin B (1 mg/kg/day).\nOn postoperative day 5, cerebrospinal fluid (CSF) obtained from lumbar puncture showed lymphocytic pleocytosis (WBC 225 cell/mm3, mononuclear cell 100%, RBC 157 cell/mm3) with increased protein of 148 mg/dl and decreased glucose levels of 27 mg/dl (serum glucose level=126 mg/dl). No organisms were identified on gram and acid-fast bacillus stain and an Indian ink preparation. CSF culture for bacteria was negative. These findings were consistent with amebic meningoencephalitis.\nIn order to identify the specific causative agent, further molecular characterization was then performed, using the formalin-fixed brain tissue and fresh CSF sample as detailed below.