Febrile infection-related epilepsy syndrome and splenial lesions: a case report and review of the literature

Purpose: We report a case of febrile infection-related epilepsy syndrome (FIRES) with a lesion in the splenium of the corpus callosum, and explore the pathophysiology by conducting a literature review.Case Report: A 10-year-old Japanese boy developed repetitive seizures after five days of febrile illness. MRI at admission revealed a splenial lesion with reduced diffusivity and low apparent diffusion coefficient. Apneic seizures with ocular gaze, facial twitching, with/without focal or bilateral tonic posturing necessitated high dose phenobarbital therapy under artificial ventilation for seven days. The splenial lesion disappeared on the follow-up MRI on day 3, but bilateral hippocampal lesions emerged on day 10. The seizures were mitigated by potassium bromide. At onset of encephalopathy, the platelet count and C-reactive protein (CRP) level were low.Methods: Data from 21 individuals with FIRES and 32 individuals with mild encephalopathy/encephalitis with reversible splenial lesion (MERS) were collected from online bibliographic databases. Onset age, prodromal period, blood cell counts, CRP, electrolytes, and liver enzymes were compared between these two groups.Results: Onset age, prodromal period, and liver enzymes were significantly higher and platelet count and CRP were lower in the FIRES group than in the MERS group.Discussion: In our case, the initial MRI findings resembled those of MERS, but the subsequent clinical course and seizure semiology, as well as blood test results were consistent with a diagnosis of FIRES. A splenial lesion in FIRES may be associated with the relatively attenuated seizure activity during the acute phase in this and another reported case, which needs further corroborations.