MERS: Mild Encephalopathy/Encephalitis with Reversible Lesions in the Splenium Another Three Cases

Introduction: The descriptive diagnosis of MERS (first used in 2004) is largely based on MRI findings: a nonenhancing, round-shaped lesion in the splenium of the corpus callosum with reduced diffusion that completely disappears within weeks. Until now, most patients have been reported in Japan, associated with viral infections (1/3 influenza viruses) causing encephalitis/encephalopathy.

Gradually, a series of noninfectious conditions have been found showing identical MRI findings: hypoglycemia, hypernatremia, seizures, antiepileptic drug treatment, extracranial neoplasm, and malnutrition. Not all patients presented with encephalopathic symptoms.

Case Reports: We present another three patients, all of them showing the radiologic characteristics of MERS, completely reversible, with quite different concomitant diseases.

A case of a 1.12-year-old boy who was febrile, mildly encephalopathic, CSF pleocytosis, no causative viral, or bacterial agent could be detected

A case of a 2.2-year-old girl with status epilepticus fibrils, enterovirus-associated encephalopathy, no CSF pleocytosis

A case of a 3.17-year-old boy who was suffering from severe hemolytic anemia, under the treatment with cortisone and plasmapheresis an encephalopathy developed.

All the three patients improved clinically and recovered within 1 week. The MRIs of all of them showed a complete remission of the brain lesions.

Discussion: The pathophysiology of the cerebral lesions is unknown. Because of the fact that the concomitant diseases are quite different (to our knowledge, a hemolytic anemia and/or its immune suppressive treatment [patient 3] has never been reported), it is difficult to speculate on a common underlying mechanism. The lesion itself seems to be a nonspecific phenomenon, causing no definite damage to the brain.