Uncommon histopathological features of cytomegalovirus encephalitis and measles inclusion body encephalitis on autopsy in two patients with primary immunodeficiency

Purpose: To describe the neu-ropathological findings in two patients with primary immunodeficiency who had fatal viral encephalitis. Materials and methods: Severe combined immunodeficiency (SCID) was confirmed in case 1 by genetic testing, while case 2 had features suggestive of com-bined immunodeficiency; however, whole exome sequencing showed no pathogenic variants. Autopsies were performed in both cases after an informed consent. A detailed sampling of the brain including extracranial organs was conducted. Immunohistochem-istry and electron microscopy was also per-formed to confirm the presence of viruses. Results: Besides evidence of cystic encepha-lomalacia observed in both cases, the brain in case 1 revealed cytomegalovirus (CMV) ventriculoencephalitis accompanied by an exuberant gemistocytic response in the en-tire white matter. Nuclei of gemistocytes were loaded with several CMV nuclear inclu-sions, which was confirmed by immunohis-tochemistry. Case 2 demonstrated features of measles inclusion body encephalitis with several viral inclusions within neurons and astrocytes. Rare giant cells were also seen. Measles virus was confirmed on immunohistochemistry and electron microscopy. Plau-sibly, there was paucity of microglial nodules in both cases. Superadded bacterial pneu-monia with diffuse alveolar damage was also seen in both cases. Conclusion: These cases add to the spectrum of unusual histo-logical features of viral encephalitis seen in patients with underlying primary immuno-deficiency diseases.