[An autopsy case of elderly-onset herpes simplex encephalitis with acute respiratory failure caused by brainstem lesions].

An 89-year-old man was admitted because of persistent fever and impaired consciousness. On admission, his consciousness level was E3V3M4 according to the Glasgow Coma Scale. MRI of the brain showed high intensity lesions in the bilateral cingulate gyri. In the cerebrospinal fluid, both cell counts and glucose level were in the normal ranges. He had received antibiotics and intravenous isotonic saline. On the fifth day of hospitalization, blood examination revealed elevation of anti-herpes simplex virus (HSV) immunoglobulin M antibody, and herpes simplex encephalitis (HSE) was diagnosed. Despite treatment with acyclovir, his respiratory function and consciousness level deteriorated rapidly. On the eighth day, he died of respiratory failure. At autopsy, the brain showed multiple softenings of the gray and white matter in the hippocampus, amygdala, and temporal, insular, and cingulate cortices. Some of these lesions were hemorrhagic. Microscopic examination revealed that the lesions were necrotic and associated with perivascular inflammatory cell infiltration in the limbic system, hypothalamus, brainstem tegmentum area, and medulla. Eosinophilic intranuclear inclusions were rarely found in the astrocytes in the medulla. Immunohistochemistry revealed anti-HSV-1 antibody positive neurons in the brainstem tegmentum including reticular formation and the raphe nuclei. HSV-DNA was also detected in the postmortem cerebrospinal fluid. This was a rare case of HSE in which inflammation in the brainstem proved to be the cause of lethal respiratory failure.