Rasmussen Encephalitis

A 10-year-old boy presented with recurrent focal seizures since the age of six, followed by progressive left sided weakness and mild cognitive decline. Now, even after treatment with anti-epileptic drugs, patient has continuous movement of tongue, lower lip, and left thumb suggestive of epilepsia partialis continua. Electroencephalogram showed unilateral right hemispheric slowing.

MRI brain was performed. T1 axial section of brain (Figure 1) shows atrophy of right cerebral hemisphere (evident by prominent right sylvian fissure) and right basal ganglia (evident by reduced size of caudate head and lentiform nucleus). Increased signal intensity is seen in fluid attenuated inversion recovery (FLAIR) axial section of brain involving right insular, peri-insular cortex and right basal ganglia (Figure 2).

Background Rasmussen encephalitis is a chronic encephalitis of unknown aetiology, which presents as drug-resistant epilepsy, progressive hemiparesis, and cognitive impairment. It has a bimodal age distribution, affecting children and young adults^1,2.

Clinical Perspective Diagnosis is made based on clinical features, serial magnetic resonance imaging (MRI), electroencephalogram (EEG) or histopathological findings. Clinical features include epilesia partialis continua and progressive unilateral focal neurological deficits with variable degree of cognitive impairment. On EEG, persistent high amplitude delta activities are noted in involved hemisphere³. Immunohistochemistry of affected cortex reveals T-cell mediated inflammatory injury^1,2. Serial MRI is invaluable in diagnosis, staging of disease, exclusion of other diagnosis and presurgical localization of involved cortex^2,4.

Imaging Perspective Imaging findings depend on the stage of the disease that are- prodromal, active, and chronic stages^1,2. Initially, unilateral focal cortical swelling may be seen. With time, T2/FLAIR hyperintensity develops in the cortex and subcortical white matter of the involved side. With progression of disease into chronic phase, unilateral cerebral and basal ganglia atrophy is seen^1,2. Predilection for peri-sylvian cortex is seen. In basal ganglia, caudate head is the preferred site of involvement¹.

In addition, newer MRI imaging techniques can help in presurgical localization of seizure focus. For example, perfusion MRI can show altered perfusion in peri-ictal and inter-ictal phases of disease⁵. Functional MRI can demonstrate eloquent areas like motor or language area with respect to the focus producing seizures so that eloquent areas could be avoided during focal cortical resection wherever possible⁶.

Outcome The natural course of disease is progressive unilateral neurologic deficits with seizures which eventually become refractory to anti-epileptic drugs and variable degree of cognitive decline. Treatment depends on clinicoradiological staging of disease. For example, in early stage, corticosteroid or immunomodulatory drugs are preferred treatment. Whereas in non-responsive chronic cases, more invasive management like focal cortical resection, hemispheric disconnection or functional hemispherectomy are being done^2,7,8.

Take Home Message / Teaching Points In the setting of typical clinical features, MRI findings of unilateral cerebral atrophy with predisposition for peri-sylvian region and atrophy of basal ganglia are highly suggestive of Rasmussen Encephalitis.