Transmantle heterotopia associated with acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) in an adolescent male patient

Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) is the most common type of acute encephalopathy. It occurs frequently in infants but rarely in teenagers. More than half of patients with AESD have neurological sequelae, but there are few, evidence-based treatments. Transmantle heterotopia is a rare type of gray matter heterotopia. We report herein a case of transmantle heterotopia with suspected involvement in AESD. A 10-year-old, male patient with developmental disabilities and a history of multiple febrile seizures was admitted for fever and convulsion. On day 2 of the fever, he experienced six, intermittent convulsions over three hours despite antiepileptic drug administration. On admission, he had impaired consciousness and was positive for influenza virus type B. Other examinations, including brain CT, found no abnormalities. After admission, targeted temperature management (TTM) and vitamin, antibiotic, and oseltamivir therapy was begun. The patient experienced a prolonged state of impaired consciousness, prompting MRI to be performed on hospital day 6. Brain MRI findings suggested AESD and transmantle heterotopia. His consciousness status gradually improved, and he was able to perform gross motor activities and engage in simple conversation. He was discharged after valproic acid administration was begun. Two months after discharge, the patient displayed heightened impulsivity. The present case of transmantle heterotopia was strongly suspected of being involved in the development of febrile status epilepticus and AESD. Children with underlying neurological disorders can experience AESD development even if they are older than the usually affected aged group.