Seizure frequency, degree of hemiparesis and cerebral hemiatrophy are analysed in 13 patients with histopathologically proven Rasmussen’s encephalitis (RE) examined at the University of Bonn, Germany. The age at first seizure was in childhood in 10 cases (range, 1.6 - 15.7 years) and in adulthood in 3 (22.1 - 40.9 years). An initial prodromal stage (Montreal Neurological Institute Stage 1), characterized by low seizure frequency, had a median duration of 7.1 months (range 0 months to 8.1 years), shorter in children than adults. An acute (MNI stage 2) phase was recognized by a rapid increase in seizure frequency (to >10 simple partial motor seizures per day) accompanied by development or deterioration of hemiparesis and loss of hemispheric volume. Initial MRI scans showed inflammatory lesions, with monofocal onset between Rolandic and temporomedial areas, which spread across the ipsilateral hemisphere. The median duration of stage 2 was 8 months (range 4-8 months). Residual phase (MNI stage 3) was marked by a relatively stable permanent hemiparesis and diminished seizure frequency.
Patients were divided into two groups, according to age, duration of prodromal stage and outcome. Type 1 patients (n=7), all children, had a more rapid and severe disease than type 2 (adolescents and adults). Type 1 cases had a median age of 5.3 years (range 1.6-6.1 years) at onset of seizures, the prodromal stage was absent or short, and the acute phase lasted 8 months (range 4-8 months). Type 2 patients (n=6) had a median age of 18.9 years (range 6.4-40.9 years) at onset, a long prodromal stage (median duration 3.2 years, range 1.3-8.1 years), focal epilepsy with complex partial or secondarily generalized tonic-clonic seizures, rare occurrence of hemiparesis, of lesser frequency and degree than type 1 patients, only 2 requiring hemispherectomy, and an acute phase lasting 7.5 months (range 7-8 months). Histopathologically, the 2 types were similar, with chronic inflammatory changes in all patients. Most of the brain damage had occurred in the first 8-12 months. 
COMMENT. The authors recommend that future therapeutic interventions should focus on the 8 month period of the acute disease phase, when the most extensive brain damage occurs. In children, this acute phase with increased frequency of seizures and development of hemiparesis occurs early and soon after the onset of seizures, whereas in adolescents and adults, the acute phase is delayed and follows a long prodromal stage. In the later residual stage, the majority of brain atrophy will have taken place, and the measurement of improvement following immunosuppressive treatment will not be possible. Estimation of hemispheric volume loss may be used as a parameter of the destructive disease process during the acute phase. An autoimmune response mediated by cytotoxic T lymphocytes is proposed as a key mechanism in the etiology of Rassmussen’s encephalitis (Bauer J, Bien CG, Lassmann H. see Ped Neur Briefs April 2002;16:27-28).