Clinically Mild Encephalitis/Encephalopathy with a Reversible Splenial Lesion due to <i>Mycoplasma pneumoniae</i> Infection

Abstract

A 30-year-old man presented with fever and consciousness disturbance (Glasgow Coma Scale; E4V1M6). Chest computed tomography showed infiltrative shadows in both lungs (Picture 1). Diffusion-weighted and T2-weighted brain magnetic resonance imaging (MRI) (Picture 2A, 2B) revealed high intensity in the splenium of the corpus callosum (SCC) (arrows). Mycoplasma pneumoniae antibody (particle agglutination) titer was markedly elevated (10,240 fold), thus M. pneumoniae pneumonia was diagnosed. After intravenous levofloxacin treatment, his consciousness disturbance was completely recovered on the third hospital day, and the SCC lesion disappeared one week later (Picture 2C, 2D), along with improvement of pneumonia. Clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) is characterized by the MRI finding of a lesion with transiently reduced diffusion, at least in SCC, and shows a favorable prognosis (1). We report the first adult case of MERS due to M. pneumoniae infection; only a few child cases have been reported to date (2).