Rasmussen Encephlalitis

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Background    Neuroimaging    Gross Pathology    Histopathology & Immunohistochemistry    Differential Diagnosis    Reference

BACKGROUND AND CLINICAL INFORMATION: Head

Summary: This is a slowly progressive neurological disease of childhood onset and characterized by intractable seizure, epilepsia partialis continua, and neurologic deterioration over months or years. Pathologicall characterized by slowly progressive, lateralized brain destruction or atrophy. Histologically characterized by an encephalitic process leading to neuronal loss, gliosis, microglial nodules and atrophy. Some cases are associated with a history of prior vaccination. No infectious agent has been identified.

Age of Onset: 6.8 ± 5.1 years

Clinical Course: Presentation is usually stereotyped. Patients, usually children with or without a preceding febrile illness initially, develop early onset of partial seizures refractory to anti-epileptic drugs. Epilepsia partialis continua (EPC) is a characteristic finding. The disease progresses slowly over months to years and often reaching a plateau after several years of intractable epilepsy. The patient will then remain stable with fixed neurologic deficits including hemiplegia, with or without aphasia, hemianopia, mental retardation and residual seizures. Rasmussen's encephalitis is compatible with long-term survival.

·         Epilepsia partialis continua EPC is a type of focal motor epilepsy characterized by persistent rhythmic clonic movements of one muscle group- usually of the face, arm, or leg- which are repeated at fairly regular intervals of a few seconds and continue for hours, days, weeks, or months without spreading to other parts of the body. Most patients with EPC show focal EEG abnormalities.

Pathogenesis: Associated with antibodies against glutamate GluR3 receptors.

NEUROIMAGING: Head

Unilateral atrophy of the cerebral hemispheres is noted on MRI or CT scan that is accompanied by corresponding remodeling of the cranium in severe cases.

GROSS PATHOLOGY: Head  

HISTOPATHOLOGY AND IMMUNOHISTOCHEMISTRY: Head

Salient Features: Chronic inflammatory process limited to one cerebral hemisphere with neuronal loss, gliosis, and extensive destruction leading to macroscopic atrophy.

Basic changes: The ultimate histopathologic changes are composed of an interplay between the four pathologic parameters below:

• Neuronal loss and gliosis

• Perivascular lymphocytes

• Subarachnoid inflammation

• Microglial nodules

Histologic Pictures:

·         Active disease: Brain tissue shows ongoing inflammatory process in which microglial nodules, with or without neuronophagia, are numerous and accompanied by perivascular chronic inflammatory cells infiltration and gliosis.

·         Active and remote disease: Brain tissue shows several microglial nodules, with perivascular chronic inflammatory cell infiltration and at least one gyral segment of complete necrosis and cavitation involving full-thickness cortex.

·         Remote disease: Brain tissue shows neuronal loss and gliosis with moderately abundant perivascular chronic inflammatory cell infiltration and few microglial nodules.

·         Nonspecific changes: Brain tissue is free of or with very minute amount of microglial nodules and mild perivascular inflammation, combined with various degrees of neuronal loss and gliosis.

DIFFERENTIAL DIAGNOSIS: Head

Russian spring-summer tick-borne encephalitis has clinical and morphologic findings similar to Rasmussen's encephalitis. It has a high incidence of EPC, chronic inflammatory changes, and protracted course. However, Russsian sping-summer tick-borne encephalitis has bilateral inflammatory change. There is also involvement of the basal ganglia and cerebellum, and the extensive proliferation of plasma cells in primate models. Ataxia is also a prominent feature.

Subacute sclerosing panencephalitis (SSPE) has large amount of plasma cells in contrast to Rasmussen's encephalitis where most inflammatory cell infiltration are lymphocytic. Cowdry type A viral inclusions occur in about 20-40% of SSPE but have never been described in Rasmussen's encephalitis. White matter lesions tend to be more severe with SSPE and unilateral hemispheric atrophy is not a feature of SSPE. Oligoclonal band can also be seen in the CSF of SSPE patients.

Prion diseases: the frequent finding of spongiosis in Rasmussen's encephalitis may suggest prion diseases. However, widespread inflammation is not seen in both Cruetzfeld-Jacob disease and Gerstmann-Str„ussler-Scheinker syndrome. Prion protein can be identified in prion diseases but not in Rasmussen's encephalitis. In addition, the survival of patients with CJD is much shorter and unilateral hemispheric atrophy is not common in prion diseases.

Progress rubella panencephalitis is a predominantly demyelinating disease of the white matter with extensive involvement of the basal ganglia and brain stem, which leaves the cerebral cortex relatively unaffected. They are characterized by a necrotizing vasculitis of white matter and basal ganglia, and is complicated by severe, anterior fibrosis and calcifiations.

Viral meningoencephalitis usually display microglial nodules and inflammation in the subacute stages. Unilateral cerebral involvement is quite unusual. Some of them may progress in a slow virus disease.

REFERENCES: Head

Rasmussen T, Olszewski J, Lloyd-Smith D. Focal Seizures due to chronic localized encephalitis. Neurology 1958; 8:435-445

Fredrick Andermann, Chronic encephalitis and epilepsy: Rasmussen's syndrome. 1991 Butterworth-Heinemann.