Mild encephalitis/encephalopathy with a reversible splenial lesion (MERS): A case report and review of the literature

Abstract

Mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) is a rare clinico-radiological syndrome characterized by transient encephalopathy associated with a reversible lesion in the splenium of the corpus callosum, most commonly occurring in the setting of infection or metabolic disturbance. We report the case of a 21-year-old male who presented with an acute generalized seizure following an influenza-like illness. Brain magnetic resonance imaging (MRI) demonstrated a well-defined ovoid lesion in the midline splenium of the corpus callosum, hyperintense on T2-weighted and FLAIR sequences, with marked diffusion restriction and corresponding low apparent diffusion coefficient (ADC) values, without contrast enhancement. Laboratory investigations, including serum studies and cerebrospinal fluid analysis, were within normal limits. The patient was managed with supportive care and antiepileptic therapy, with complete clinical recovery. Follow-up MRI performed after recovery demonstrated complete resolution of the splenial lesion, confirming its transient nature. This case highlights the importance of recognizing MERS in young patients presenting with post-infectious altered consciousness or new-onset seizures and underscores the central role of MRI in establishing the diagnosis and excluding other causes of splenial diffusion restriction.