Longitudinal PET and MRI Evaluation in Late Onset Rasmussen Encephalitis: A Series of Three Cases

Rasmussen's encephalitis (RE) is a rare, chronic, neurological disorder characterized by progressive focal epilepsy and hemispheric atrophy. Late-onset RE poses diagnostic challenges due to atypical clinical features and nonspecific early MRI findings.

This case series underscores the value of [18F]FDG PET in detecting unihemispheric hypometabolism and crossed cerebellar diaschisis at diagnosis, before MRI changes appear.

During follow-up, PET identified active disease through hypermetabolic foci or pseudo-normalized metabolism, indicative of subclinical seizures, while stable hypometabolism signaled quiescence.

Combining PET with MRI enhances diagnostic accuracy and guides treatment decisions in managing RE.