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Rasmussen encephalitis, also known as chronic focal encephalitis, is a chronic inflammatory disease of unknown origin, usually affecting one brain hemisphere.
It is not to be confused with a Rasmussen aneurysm.
Most cases (85% cases) occur in children under the age of 10 years 1. However, detection in adults is increasing with routine MRI investigations for intractable seizures 5.
Patients frequently have episodes of epilepsia partialis continua or generalized status epilepticus, although the latter is less common. The seizures are often intractable despite aggressive medical management 1.
Apart from seizures, the patient may have hemiparesis, speech disturbances, and hemianopia, each pertaining to unilateral cerebral involvement. Cognitive impairment over time may also be seen, especially in a patient presenting later in adolescence.
Pathologic features are similar to viral encephalitis, with lymphocytes surrounding round cells and diffuse proliferation of microglia. However, later spongiform degeneration and cortical atrophy set in.
The observed inflammatory changes in Rasmussen encephalitis include perivascular cuffing, microglial nodules, T-lymphocytic infiltration gliosis, meningeal inflammation, and neuronal injury or loss 9,10.
An autoimmune mechanism has also been proposed describing antibodies against the GluR3 subunit of the α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor in a few patients 11.
The exact cause of the disease is unknown. However, various viral (SSPE-like, EBV or CMV) or inflammatory episodes have been implicated by different authors 3,4,6.
Radiographic features are usually isolated to a single hemisphere; however, bilateral Rasmussen encephalitis has also been described in numerous case reports 12-14.
CT may not show any specific feature in early imaging; however, patchy hypodense attenuation areas (similar to viral encephalitis) may be seen. The late-stage disease may show unilateral cortical atrophy. CT perfusion may show decreased cerebral blood flow (CBF) 1.
Atrophy is typically earliest appreciated in the ipsilateral caudate nucleus, before atrophy and signal changes are appreciated more generally in the hemisphere. Signal characteristics include:
- T1: unilateral cortical atrophy with ex vacuo ventricular dilatation 15
- T2: hyperintense signal areas in the affected hemisphere 15
- DWI/ADC: restricted diffusion may be seen in altered signal areas 15
- T1 C+ (Gd): no significant post-contrast enhancement 15
Treatment and prognosis
Treatment with high-dose methylprednisolone and intravenous immunoglobulin has been positive, further supporting the autoimmune nature of the disease 16,17. Anti-seizure medications have a limited symptomatic role 17.
Hemispherectomy or functional hemispherectomy are the only definitive treatments in refractory cases, which resolves seizure activity or significantly decreases seizure frequency in most patients 16.
History and etymology
It was first described by Theodore Brown Rasmussen (1910-2002), American neurologist, in 1958 2.
General imaging differential considerations include:
- 1. Tien RD, Ashdown BC, Lewis DV et-al. Rasmussen's encephalitis: neuroimaging findings in four patients. AJR Am J Roentgenol. 1992;158 (6): 1329-32. AJR Am J Roentgenol (abstract) - Pubmed citation
- 2. Rasmussen T, Olszewski J, Lloyd Smith D. Focal seizures due to chronic localized encephalitis. Neurology. 2000;8 (6): 435-45. Pubmed citation
- 3. Rasmussen T, Andermann F. Update on the syndrome of "chronic encephalitis" and epilepsy. Cleve Clin J Med. 1989;56 Suppl Pt 2 : S181-4. - Pubmed citation
- 4. Farrell MA, Cheng L, Cornford ME et-al. Cytomegalovirus and Rasmussen's encephalitis. Lancet. 1991;337 (8756): 1551-2. Lancet (link) - Pubmed citation
- 5. Mclachlan RS, Girvin JP, Blume WT et-al. Rasmussen's chronic encephalitis in adults. Arch. Neurol. 1993;50 (3): 269-74. Arch. Neurol. (link) - Pubmed citation
- 6. Atkins MR, Terrell W, Hulette CM. Rasmussen's syndrome: a study of potential viral etiology. Clin. Neuropathol. 14 (1): 7-12. - Pubmed citation
- 7. Oguni H, Andermann F, Rasmussen TB. The syndrome of chronic encephalitis and epilepsy. A study based on the MNI series of 48 cases. Adv Neurol. 1992;57: 419-33. Pubmed citation
- 8. Sethi NK, Tenney JR. Child Neurology: Hemiconvulsion-hemiplegia-epilepsy syndrome. Neurology. 2012;79 (24): 2367. doi:10.1212/01.wnl.0000424157.07211.bf - Pubmed citation
- 9. Rasmussen T, Olszewski J, Lloydsmith D. Focal seizures due to chronic localized encephalitis. Neurology. 2000;8 (6): 435-45. Pubmed citation
- 10. Bien CG, Bauer J, Deckwerth TL et-al. Destruction of neurons by cytotoxic T cells: a new pathogenic mechanism in Rasmussen's encephalitis. Ann. Neurol. 2002;51 (3): 311-8. Pubmed citation
- 11. Rogers SW, Andrews PI, Gahring LC et-al. Autoantibodies to glutamate receptor GluR3 in Rasmussen's encephalitis. Science. 1994;265 (5172): 648-51. Pubmed citation
- 12. Guan Y, Luan G, Zhou J, Liu X. Bilateral Rasmussen encephalitis. Epilepsy & behavior : E&B. 20 (2): 398-403. doi:10.1016/j.yebeh.2010.12.004 - Pubmed
- 13. Tobias SM, Robitaille Y, Hickey WF, Rhodes CH, Nordgren R, Andermann F. Bilateral Rasmussen encephalitis: postmortem documentation in a five-year-old. Epilepsia. 44 (1): 127-30. Pubmed
- 14. Peariso K, Standridge SM, Hallinan BE, Leach JL, Miles L, Mangano FT, Greiner HM. Presentation, diagnosis and treatment of bilateral Rasmussen's encephalitis in a 12-year-old female. Epileptic disorders : international epilepsy journal with videotape. 15 (3): 324-32. doi:10.1684/epd.2013.0594 - Pubmed
- 15. Faria AV, Reis F, Dabus GC, Zanardi VA, Guerreiro MM, Cendes F. MRI findings in the diagnosis and monitoring of Rasmussen's encephalitis. Arquivos de neuro-psiquiatria. 67 (3B): 792-7. Pubmed
- 16. Bien CG, Granata T, Antozzi C et-al. Pathogenesis, diagnosis and treatment of Rasmussen encephalitis: a European consensus statement. Brain. 2005;128 (3): 454-71. doi:10.1093/brain/awh415 - Pubmed citation
- 17. Varadkar S, Bien C, Kruse C et al. Rasmussen's Encephalitis: Clinical Features, Pathobiology, and Treatment Advances. Lancet Neurol. 2014;13(2):195-205. doi:10.1016/S1474-4422(13)70260-6 - Pubmed