Mild Encephalitis/Encephalopathy with a Reversible Splenial Lesion in an Adult Patient with Influenza

We herein report the case of a 31-year-old Japanese woman who developed adult-onset clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) and presented with consciousness disorder and olfactory disturbance secondary to influenza A infection. The patient's neurological symptoms and the lesion in the splenium resolved within 14 days without therapy. Magnetic resonance images and the clinical course were consistent with a diagnosis of MERS; however, mental changes following the influenza infection always present a diagnostic dilemma for physicians. We considered various diagnoses, including viral encephalitis, medication-related encephalopathy, and MERS. A comprehensive assessment may be required to diagnose MERS, since it may mimic other neurological diseases, such as viral encephalitis and medication-related encephalopathy.