Mild encephalitis/encephalopathy with a reversible splenial lesion in children

Authors, most of them Japanese, have recently published an increasing number of articles on mild encephalitis/encephalopathy with a reversible splenial lesion. We report on two new white European patients and compare published data with our own observations. A 15-year-old girl developed headache, fever, dizziness, vomiting and nuchal rigidity over four days. CSF showed elevated protein and cell count, with the lowest serum Na being 131 mmol/L. MRI on day seven was normal, but she remained febrile, had cerebral edema and episodes of confusion. MRI on day 11 showed a small T2-hyperintense lesion with restricted diffusion in the callosal splenium. Adenoviral infection was proved, and the girl underwent a protracted course of recovery. MRI signal changes improved in six days and disappeared after four months. A 12.5-year-old girl developed headache, lethargy, drowsiness and vomiting. On day five she experienced right-sided numbness, weakness and inability to speak which lasted 12 hours. She was confused and disoriented. MRI disclosed a tiny area of increased T2-signal and restricted diffusion in the splenium. Serum Na was 133 mmol/L, CSF cell count and protein was markedly elevated, and enteroviral infection was detected. Echocardiography showed no changes predisposing to clot formation and no thrombophilia was found. Her symptoms resolved in a week and MRI was normal two months later. These two non-epileptic children increase the small number of white European patients with MERS reported so far. Both had hyponatremia and encephalitis and patient 2 had transient ischemic attack, possibly due to the cerebral edema also resulting in the splenial lesion.