Rationale: Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) has been reported almost exclusively in the Japanese population.
Patient concerns: A 17-month-old male patient presented with fever and seizures, and subsequently fell into a coma. On the second day, he recovered consciousness. On the fourth day, he developed complex partial seizures and fell into a coma again. On day 10, the fever and seizures subsided. Head computed tomography on the first day showed no abnormalities. Brain diffusion-weighted images on the fourth day revealed reduced diffusion in the bilateral subcortical white matter.
Diagnosis: A diagnosis of AESD was made.
Interventions: The patient was treated with corticosteroids and intravenous immunoglobulin.
Outcomes: At the 4-month follow-up, the patient was able to walk independently, and the epileptic seizures were well controlled.
Lessons: AESD is a rare entity, and treatment with corticosteroids and intravenous immunoglobulin can lead to a favorable prognosis. Clinicians should be aware of this condition, and clinicoradiological features can suggest the diagnosis.