Rasmussen Encephalitis (RE) is a rare, chronic immune-mediated neurological disease that is typically characterized by inflammation of the cerebral cortex in one hemisphere. RE typically affects children under 10 years old, but it may rarely occur in adolescents and adults; however, despite primarily affecting children, RE is considered to be a sporadic disease, as a genetic component has yet to be identified.
The presentation of RE may occur in various degrees of speed and severity, depending on the individual. Initially, there is a prodromal stage, characterized by occasional seizures and rarely hemiparesis for about 7 months. Approximately 1/3 of patients present in the second stage, or acute stage, which usually lasts about 4-8 months. It is characterized by frequent seizures, and neurological damage may present as progressive hemiparesis, hemianopia, cognitive deterioration and aphasia if the language-dominant hemisphere is effected. In the final, residual stage, patients do not have as many seizures as the acute stage, but there are still quite frequent. The neurological deficits stabilize, but unfortunately remain permanent. The seizures are most often simple complex seizures, specifically called epilepsia partialis continua (EPC), and are treatment resistant. Other seizures such as general status epilepticus may occur, but it is rare.
On T1 MRI, cortical atrophy can be seen in the affected hemisphere with ex vacuo ventricular dilatation. With galladium contrast, no significant post-contrast enhancement should be observed. On T2 imaging, hyperintense signal areas can be seen in the ipsilateral hemisphere, along with atrophy of the head of caudate nucleus, and hemispheric atrophy. It has also been reported that in the initial 4 months of disease, unilateral enlargement of the inner and outer CSF compartments, mainly in the insular and peri-insular regions, may be present along with increased cortical and/or subcortical T2 and FLAIR signal. Futhermore, altered signal areas may show evidence of reduced diffusion on DWI/ADC.
References:
1. C. G. Bien, T. Granata, C. Antozzi, J. H. Cross, O. Dulac, M. Kurthen, H. Lassmann, R. Mantegazza, J.-G. Villemure, R. Spreafico, C. E. Elger; Pathogenesis, diagnosis and treatment of Rasmussen encephalitis: A European consensus statement, Brain, Volume 128, Issue 3, 1 March 2005, Pages 454–47
2. https://www.encephalitis.info/rasmussens-encephalitis
3. Faria, Andréia V., Reis, Fabiano, Dabus, Guilherme C., Zanardi, Verônica A., Guerreiro, Marilisa M., & Cendes, Fernando. (2009). MRI findings in the diagnosis and monitoring of rasmussen's encephalitis. Arquivos de Neuro-Psiquiatria, 67(3b), 792-797. https://dx.doi.org/10.1590/S0004-282X2009000500002