Epilepsia partialis continua and unilateral cortical-subcortical FLAIR-hyperintense lesion in Rasmussen's encephalitis: Is it diagnostic?

Objective: Rasmussen encephalitis (RE) is a focal encephalitis, characterized by epilepsia partialis continua (EPC) with or without seizures and progressive unilateral deficits. Imaging characteristics of RE have been rarely described in detail in relation to EPC. So, the study aimed to explore if any relationship exists between the imaging characteristics and the presence or evolution of EPC in patients with RE.

Methods: This retrospective study included 11 patients with RE fulfilling the European consensus statement on RE followed between 2015 and 2020.

Results: The mean age for onset of seizures was 12 years (range 2.5-24 years). Seven patients had limb EPCs, two had face EPCs, face, and limb EPC in one, and lingual EPC in one patient. The first MRI was done within 1 day to 1 month of the onset of seizures. It was normal in two patients and showed only cortical atrophy, focal or hemispheric in four patients, caudate atrophy in two, and cortical or subcortical hyperintensity (HI) in six patients. Follow-up MRI, within 3 weeks to 6 months of the onset of EPC (mean 1.6 months) showed paramedian frontal HI with limb EPC in six patients. Insular HI in four patients; two had facial EPCs while lingual EPC and limb EPC with facial EPC was observed in one patient each.

Significance: Fluid-attenuated inversion recovery (FLAIR) HI and focal cortical atrophy on MRI is the most common finding in the early course of RE. T2 and FLAIR hyperintensity in the paramedian frontal or insular cortex may antedate the onset of EPC or may occur simultaneously with EPC.