Chapter 37: Rasmussen Syndrome

OVERVIEW

Rasmussen syndrome (RS) or Rasmussen encephalitis (chronic encephalitis and epilepsy) was first described by Rasmussen et al in 1958.¹ It is an unusual condition typically developing in childhood, and is characterized by the occurrence of refractory partial epilepsy, often with epilepsia partialis continua (EPC), associated with progressive hemiparesis and cognitive impairment. Changes of unilateral hemispheric atrophy are seen on neuroimaging.

CLINICAL PRESENTATION

Based on the largest available patient series, the "average" RS patient can be described as follows: he or she (there is no gender predominance in RS) starts experiencing intractable unilateral focal motor seizures or temporal lobe seizures at the age of 6 years. Later on, when the inflammatory process spreads across the affected hemisphere, new seizure semiologies indicating new epileptogenic areas are observed. EPC, that is, more or less continuous myoclonic twitching of the distal extremities or the face, is frequent. Within a few months of epilepsy onset there is a progressive loss of neurological function associated with one hemisphere, typically hemiparesis, hemianopia, and (if the dominant side is affected) aphasia.^2,3

Serial brain magnetic resonance imaging (MRI) shows focal cortical and subcortical signal increase on T2 and fluid attenuated inversion recovery (FLAIR) images followed by progressive, centrifugal hemiatrophy of the cerebral hemisphere contralateral to the affected side of the body. The initial changes are usually peri-Sylvian; a frequent early MRI feature is volume loss of the head of the ipsilateral caudate nucleus.^4,5 After a year or so, the main decline remits, and there is a residual stage of stable neurological deficit and cerebral hemiatrophy. Seizure frequency remains high but is lower than in the "acute stage."³ In reality, this "average" or "typical" RS patient is uncommon. Due to the complexity of potential symptoms, the presentation of RS can take a variety of different forms.

LESS COMMON PRESENTATIONS OF RS

Since the original description of RS, other presentations have been recognized. Although RS typically develops in children, a similar presentation has been described in adults.^6,7,8 although the course is often slower and less severe. Villani et al distinguished two phenotypes in adults: an "epileptic" form characterized by focal motor epilepsy refractory to antiepileptic drug treatment, and a "myoclonic" form with EPC and/or unilateral cortical myoclonus (focal or multifocal).

Although secondary spread of seizures to the contralateral side, or a minor degree of contralateral atrophy is sometimes seen in patients with RS, true bilateral involvement in the form of bilateral inflammation has only rarely been described,^9,10 and no case of subsequent spread to the opposite side has been reported following the successful surgical treatment of unilateral RS.¹¹ The bilateral nature of RS is usually apparent within 13 months of onset of the disorder.

Dual pathology, in which there is ...