To report a rare case of granulomatous amebic encephalitis caused by Balamuthia mandrillaris in an immunocompetent patient.

Granulomatous amebic encephalitis (GAE) is an exceedingly rare disease with a mortality rate of over 90%. It can be caused by species such as Balamuthia mandrillaris, Acanthamoeba, or Sappinia pedata. Unlike primary amebic meningoencephalitis (PAM), which typically presents with an acute progression resulting in multiple lesions, GAE often follows a subacute to chronic course and is typically associated with a single space occupying lesion. Environmental exposures, including water, soil, and dust, are potential risk factors for amebic inoculation. Our case illustrates a novel presentation of amebic encephalitis that was misdiagnosed as herpes simplex virus (HSV) encephalitis.

GAE is often a fatal diagnosis due to its rapid progression and the challenges of early diagnosis. We hope this case underscores the importance of considering amebic encephalitis as a differential diagnosis, particularly when a patient does not respond to conventional broad-spectrum meningitis/encephalitis therapy.