Unmasking Balamuthia mandrillaris Through PCR in a Case of Multifocal Brain Lesions.

Balamuthia mandrillaris is a rare free-living amoeba that causes granulomatous amoebic encephalitis (GAE), a frequently fatal central nervous system infection. Diagnosis is often delayed because of nonspecific clinical presentation and radiographic findings. We describe a 70-year-old man with recent soil exposure in rural Mexico who developed progressive neurologic decline and multifocal enhancing brain lesions initially concerning for malignancy. Extensive infectious, oncologic, and autoimmune evaluations were unrevealing. Brain biopsy demonstrated dense granulomatous inflammation without identifiable organisms on routine stains. Definitive diagnosis was established via 18S rRNA PCR testing of brain tissue and subsequently confirmed by the Centers for Disease Control and Prevention. A multidrug regimen including miltefosine and investigational nitroxoline was initiated but was complicated by renal and hepatic toxicity. Despite transient radiologic improvement, the patient experienced progressive disease and ultimately died. This case underscores the diagnostic difficulty of Balamuthia encephalitis and highlights the essential role of molecular diagnostics in identifying rare pathogens when conventional testing is inconclusive.