Differences in the time course of splenial and white matter lesions in clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS).

Two patients with clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) exhibiting lesions in the white matter and entire corpus callosum (type 2) are reported. The time course differed between the splenial lesion and other lesions in the white matter and corpus callosum other than the splenium; the latter disappeared earlier than the former. These findings strongly suggest that MERS type 2 resolves completely through MERS type 1 exhibiting an isolated splenial lesion, and MERS types 1 and 2 have the same pathophysiology. The possible prior white matter lesions in patients with MERS type 1 may explain the neurological symptoms or EEG abnormalities.