[Febrile infection-related epilepsy syndrome (FIRES) with the claustrum sign in a 55-year-old woman: a case report].

A 55-year-old woman presented to our clinic with refractory status epilepticus, which developed after her symptoms of influenza had initially improved. Despite various tests, the definite cause could not be identified; however, her clinical presentation preceded by a febrile infection was consistent with that of febrile infection-related epilepsy syndrome (FIRES), a subtype of new-onset refractory status epilepticus (NORSE). Because the brain MRI on day seven revealed a claustrum sign, we administered aggressive immunotherapy. Thereafter, the patient recovered from status epilepticus, and the claustrum sign disappeared on brain MRI. Although the retrograde amnesia and chronic epilepsy persisted, the patient recovered and was able to live at home upon discharge. In patients with refractory status epilepticus that develops after a preceding infection, FIRES should be considered in the differential diagnosis regardless of age at onset, and early aggressive immunotherapy should be considered, especially in patients with a claustrum sign.