Transient hemiparesis and hemianesthesia in an atypical case of adult-onset clinically mild encephalitis/ encephalopathy with a reversible splenial lesion associated with adenovirus infection.

We herein report the case of a previously healthy 24-year-old Japanese woman who developed adult-onset clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) presenting with hemiparesis and hemianesthesia secondary to adenovirus infection. The patient's neurological symptoms and the lesion in the splenium resolved within 17 days without therapy. The radiographic features and clinical course observed in this case were consistent with a diagnosis of MERS; however, the only neurological symptoms were hemiparesis and hemianesthesia. This is the first reported case of MERS involving only hemiparesis and hemianesthesia at onset. This case suggests that a diagnosis of MERS should be suspected in patients with hemiparesis and hemianesthesia, especially when these conditions are preceded by infection.