Refractory status epilepticus with fever due to mumps vaccine-induced encephalitis caused secondary encephalopathy mimicking acute encephalopathy with biphasic seizures and late reduced diffusion

BackgroundEncephalitis due to vaccination for mumps is a rare complication that occurs in 0.00004% of recipients, and there has been no report of serious neurological sequelae. Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) has been reported as the most frequent type among acute encephalopathy syndromes in the pediatric population in Japan. There has been no report of AESD caused by vaccinations.Case presentationWe present the clinical course of a 1-year and 10-month-old boy who had no preexisting condition, and developed mumps vaccine-induced severe primary encephalitis. Refractory status epilepticus due to encephalitis persisted for 16 h and resulted in secondary encephalopathy as a form of AESD mimic. He had serious neurological sequelae, such as West syndrome, transient spastic tetraplegia, and intellectual disability, despite intensive treatments.DiscussionThe presented boy is the first patient to develop mumps vaccine-induced primary encephalitis with severe central nervous system (CNS) damage. Screening of the immunological background in the presented patient revealed no abnormalities; therefore, it is unclear why he developed such severe adverse events. In patients with acute encephalitis caused by the herpes simplex virus 1, inborn immune errors in CNS based on mutations in single genes are involved in its pathophysiology. Consequently, some immunogenetic alterations could be found by further analysis in the presented patient.