1. Presented by Bartholomew White, MD and reviewed by Heba Mostafa, MBBCh, PhD.

A patient with a past medical history of chemotherapeutic immunosuppression presents with three days of fevers. The patient was found to have neutropenia and was admitted for neutropenic fever in the setting of immunosuppressive chemotherapeutics. During the hospital stay, the patient developed confusion and lethargy. The patient then progressed into a comatose state, and died shortly after. Medical imaging during the hospital course was unrevealing. Testing the CSF for the encephalitis panel was not performed due to concerns for increased intracranial pressure.

An autopsy was performed, and there were no external macroscopic neuropathological abnormalities. The brain was serially sectioned in the coronal plane to reveal focal darkening of the white matter in a periventricular distribution. Microscopic examination demonstrated reactive changes and the following cytological changes within the brainstem.



Question: What is the most likely causative infectious agent?