Non-granulomatous meningoencephalitis with Balamuthia mandrillaris mimicking a tumor: First confirmed case from Pakistan

Background: Free-living amoebae rarely instigate intracranial infections that may resemble neoplastic conditions on imaging. Naegleria fowleri precipitates an acute, swiftly fatal meningoencephalitis, whereas Acanthamoeba and Balamuthia species typically manifest with a less aggressive onset but carry equally dire consequences. Case Description: The case describes a 33-year-old woman with subacute encephalitis caused by Balamuthia mandrillaris. She experienced 2 months of back pain, 1 month of headaches, and 2 weeks of vomiting without fever, recent travel, aquatic activities, or animal exposure. Brain magnetic resonance imaging revealed a sizable, heterogeneous enhancing mass in the right temporal and frontal lobes, accompanied by vasogenic edema and midline shift. Histopathology showed marked inflammation and damage to blood vessels with amoebic trophozoites present. The trophozoites displayed specific characteristics, leading to the diagnosis of amoebic meningoencephalitis. Polymerase chain reaction and Sanger sequencing confirmed B. mandrillaris infection while testing for N. fowleri and Acanthamoeba was negative. Despite antibiotic treatment, the patient's condition deteriorated rapidly, resulting in death within 2 weeks of presentation. Conclusion: This is the first confirmed case of B. mandrillaris central nervous system (CNS) infection from Pakistan. The incidence of this disease is expected to rise due to increasing temperatures due to climate change and the deteriorating quality of the water supply. Balamuthia meningoencephalitis should, therefore be on the differential for non-neoplastic CNS lesions. Furthermore, an atypical histopathologic picture, including the absence of granulomatous inflammation, needs to be recognized.