An infection known to be a major cause of mild encephalitis/encephalopathy with a reversible splenial lesion (MERS). Rapidly progressive dementia is a neurological condition in which dementia progresses in a short period of time.

We report on a 78-year-old woman presenting with a rapid decline in cognitive function resulting from a scrub typhus infection. Diffusion weighted images showed a signal intensity at the splenium, and subcortical white matter of both hemispheres suggesting MERS. On the neuropsychological test, the patient showed frontal executive dysfunction.

This case suggests that diagnosticians should consider the possibility that a MERS patient with a rapidly cognitive decline could have a scrub typhus infection because early diagnosis of scrub typhus is very important in this aspect of the treatment.