Rasmussen Encephalitis

Rasmussen’s encephalitis (RE) is a severe, rare, chronic inflammatory brain disease resulting in drug-resistant epilepsy and progressive destruction of one hemisphere with loss of neurological function. RE is associated with deterioration of background EEG activity, progressive atrophy on MRI, and extensive PET hypometabolism over the affected hemisphere. The disease progresses more rapidly in younger children compared to older individuals, wherein the progression is slower and atypical forms may be observed. RE is an immune-mediated disease, with a predominant role of CD8+ T cytotoxic cells and microglial cells, as well as activation of inflammasome pathway leading to an inflammatory and hyperexcitable neural environment. The initial trigger of this inflammatory/autoimmune cascade remains unknown and may be favored by some factors such as underlying brain lesion, comorbid autoimmune disease, and/or genetic predisposition. The diagnosis is based on clinical (intractable epilepsy and neurological deterioration), electrophysiological (unilateral EEG slowing), and MRI (hemiatrophy) criteria, sometimes complemented by histological documentation. Antiseizure medications are generally unable to stop seizures and the most effective procedure is the hemispherotomy (surgical disconnection of one cerebral hemisphere), which is associated with unavoidable permanent motor and neurological deficits. Immunotherapies could be used in the early stages of the disease or in patients with mild deficits that are not eligible for hemispherotomy. Based on the underlying pathophysiology, several immunotherapies have been tried in RE (none exhaustively: corticosteroid, intravenous immunoglobulins, adalimumab, tacrolimus, and azathioprine) with various results.