Balamuthia mandrillaris Encephalitis in a 12-Year-old Girl: Report of the First Case Diagnosed in Greece

To the Editors: Balamuthia mandrillaris is a free-living ameba commonly found in soil and freshwater. The ameba can act as an opportunistic pathogen in humans1 and cause a rare and usually fatal form of encephalitis, which is called Balamuthia amebic encephalitis (BAE). BAE has been reported in both immunocompromised and immunocompetent individuals.2,3 Approximately 200 cases of BAE have been documented globally, mostly in Latin America and the southwestern United States4 affecting all ages.5 The case fatality rate exceeds 90%.5 Due to the rarity of this infection and the fact that it shares clinical and radiological findings with other diseases, a prompt diagnosis can be very challenging. Remarkably, there is currently no established, evidence-based treatment protocol. We report, the first case of BAE in Greece, in a 12-year-old girl. In April 2024, a previously healthy 12-year-old girl from a Greek island presented with acute headache and left-sided hemiparesis. Brain magnetic resonance imaging (MRI) revealed a right frontal lobe lesion (3.72 cm × 3.1 cm), initially suspected to be a tumor (Fig. 1). The lesion was surgically resected, and initial recovery was good. However, histopathology showed no malignant tumor components, but areas of extensive cell necrosis, infiltrated by numerous lymphocytes, plasma-cells and eosinophils (Fig. 2). Multinucleated giant cells, Langerhans cells and several uninuclear eukaryotic cells, morphologically compatible with free living amebas were also observed, suggesting a free-living ameba infection (Fig. 2). Thirty-three days after symptom onset, the patient was readmitted with new neurological signs. Blood tests, cerebrospinal fluid analysis, flow-cytometry and immunodeficiency screening were unremarkable. Tumor markers were negative. Further MRI scans revealed 4 new brain lesions (Fig. 1). Initial empirical antimicrobial therapy was started. Polymerase chain reaction (PCR) tests for Acanthamoeba spp. and Entamoeba histolytica were negative. After consultation with the Centers for Disease and Control Prevention, a more targeted treatment regimen was initiated, including miltefosine, sulfadiazine, voriconazole, pentamidine and azithromycin. Additional brain tissue samples were obtained for histopathological and molecular testing. DNA was extracted from fresh frozen brain tissue and real-time PCR targeting the 18srRNA of B. mandrillaris was performed, as previously described.6 All brain biopsy specimens tested positive, confirming the diagnosis of BAE. Despite aggressive treatment, her condition rapidly deteriorated to quadriplegia and multiple cranial nerve palsies. A trial with nitroxoline was attempted,7 but follow-up MRI on day 60, showed widespread brain lesions and leptomeningeal inflammation (Fig. 1). The girl developed respiratory distress, was intubated, and admitted to the intensive care unit. She died on day 75, 41 days after her second admission.FIGURE 1.: A: T1-weighted transverse image after the intravenous administration of gadolinium, revealing a right frontal lobe space-occupying lesion with irregular enhancement (Day 3). B: T2-weighted image of the same area showing extensive vasogenic edema (hyperintense signal) surrounding the aforementioned lesion as well as midline shift towards the left hemisphere (Day 3). C: T2 weighted transverse image showing 2 new lesions in the right and left posterior frontal lobes surrounded by lesser edema (postsurgical findings are also visible, such us fluid effusions below the craniotomy and at the site of excision) (Day 33). D: Coronal image of the same scan (FLAIR sequence) revealing 1 more lesion in the left temporal lobe (Day 33). E: T2-weighted transverse image showing patches of edema surrounding multiple new lesions located in the cerebral hemispheres as well as the basal ganglia (Day 60). F: T1 weighted transverse image of the same slice showing ring-enhancement in some of the lesions and areas of leptomeningeal enhancement (most notably in the bilateral frontotemporal regions) (Day 60). G: FLAIR image of the sagittal plane revealing extensive new lesions, including lesions in the cerebellar hemispheres (Day 60). H: Another sagittal FLAIR image of the same sequence, revealing the involvement of the corpus callosum, the right thalamus and the cerebellum (Day 60).FIGURE 2.: A, B: Trophozoites of Balamuthia in the brain caused meningoencephalitis. The trophozoites are spherical or oval cells with a single round nucleus (Giemsa staining × 40). They have a thin cell membrane and finger-like projections (pseudopodia). The cytoplasm contains vacuoles (Masson’s trichrome × 40). C: Granulomatous reaction with mixed inflammatory cells, histiocytes and multinucleated giant cells around Balamuthia trophozoites (Hematoxylin and Eosin × 40). D: Phagocytosis of a Balamuthia trophozoite by a multinucleated giant cell (Hematoxylin and Eosin × 40). E, F: Balamuthia cyst within a multinucleated giant cell (Hematoxylin and Eosin × 40, Giemsa × 40).The challenges we encountered in diagnosing and treating this first case of BAE in Greece highlight the difficulties presented worldwide by this rare and lethal infection. The true incidence of BAE is likely underestimated due to low clinical awareness. The molecular detection of Balamuthia in environmental samples from Europe indicates the parasite is present in both rural and urban areas, although its precise ecological niche is to be determined.8 The parasite invades the central nervous system via the bloodstream or nasal mucosa.9 In this case, infection likely occurred through environmental exposure. BAE presents with nonspecific neurological symptoms and is difficult to diagnose clinically. Cerebrospinal fluid findings are often inconclusive. Diagnosis relies on brain biopsy and PCR, but delays are common. Treatment lacks standardized protocols; early multidrug therapy may help, though survival remains rare and outcomes are often poor. Next-generation sequencing offers hope for faster diagnosis, and omics-based research may lead to more effective therapies.10 In conclusion, more research is needed to identify effective therapies, understand risk factors for disease progression and improve diagnostic tools. Increased clinical awareness is essential, even in nonendemic areas, as B. mandrillaris may be more widespread than currently recognized. ACKNOWLEDGMENTS The authors thank Professor George L. Daikos, for his invaluable clinical insights and help in diagnosing this case.