Brainstorm: A case of granulomatous encephalitis

Free-living amoebas (FLA) can cause severe and fatal central nervous system infections that are difficult to diagnose. We present the case of a 74-year-old immunocompetent woman admitted for focal neurological symptoms with enhancing lesions in the right cerebellar hemisphere. A first cerebral biopsy showed granulomatous inflammation, but no microorganisms were identified. After transient clinical improvement, she eventually deteriorated 4 months after initial presentation, with an MRI confirming multiple new masses affecting all cerebral lobes. A second brain biopsy revealed granulomatous and acute inflammation with organisms containing a large central nucleus with prominent karyosome, consistent with free-living amoebas. Immunohistochemical and polymerase chain reaction assays performed at CDC were positive for Acanthamoeba spp., confirming the diagnosis of granulomatous amoebic encephalitis (GAE) caused by Acanthamoeba spp. The patient was treated with combination therapy recommended by CDC, but unfortunately died a few days later. Upon histopathological rereview, amoebic cysts and trophozoites were identified by histochemical and immunohistochemical methods in the first cerebral biopsy. FLA infections can be challenging to diagnose because of the low incidence, the non-specific clinical and radiological presentation, the lack of accessible diagnostic tools, and clinicians’ unfamiliarity. This case highlights the importance of recognizing FLA as a potential cause of granulomatous encephalitis, even in the absence of risk factors, as early treatment might be associated with favorable outcomes in case reports. When suspected, CDC laboratories offer tests to confirm the diagnosis promptly.