Autism and epilepsy

The disorders of the autistic spectrum are severe, chronic neurobiological disorders with a frequency of at least one case per 500. The diagnosis is made in early life as the patients develop reduced social interaction and communication, along with a preference to stereotypic and isolated activities. In most patients a delay in verbal and non-verbal communication is observed, while some patients never achieve useful language.

About 20 to 30% of the patients with autism have epileptic seizures as well. More likely to develop epilepsy are female patients, those with severe cognitive defects, verbal auditory agnosia, motor handicaps, as well as those with a family history of epilepsy. The onset of epileptic seizures is either at early childhood or at the age of puberty. Patients with autism and epilepsy may develop all type of seizures and some patients do present more than one seizure types.

The etiology of this co-morbidity (autism and epilepsy) is in most cases unclear. In some cases both conditions may be entirely independent and acquired together by chance. In other cases autistic phenotype and epilepsy are associated, both being independent consequences of the same genetic disorder (e.g. fragile-X syndrome, Rett syndrome) or the same acquired early cerebral insult (e.g. congenital rubella). In such cases, the epileptic seizures or epileptiform discharges are the markers of an underlying cerebral pathology that modifies the threshold of neuronal excitability, either focally or diffusely, but they have no direct causal role in the autistic behavior. This is probably the most frequent situation, keeping in mind that severe or frequent seizures may worsen some aspects of cognitive and motor function in an autistic child, as it can happen in non-autistic intellectually disabled children. In a number of cases the epileptic process interferes directly with the function of specific networks involved in the development of human communication and social behavior. In these cases, the underlying pathology (which is either known- e.g. a focal cortical dysplasia- or of unknown origin) is not directly responsible for the autistic phenotype but for the epilepsy it triggers. Bilateral hippocampal sclerosis after a prolonged status epilepticus or sustained bilateral epileptic discharges from the frontal or temporal areas may have a similar effect. The epileptic process spreads to structures thought to be dysfunctional in autism, like orbitofrontal cortex, anterior cingulate gyrus or amygdale that belong to the limbic system, possibly at a critical period of the maturation, and generates the autistic symptoms. These networks may already be abnormal for some reason (genetic or early damage) and thus be at the origin of a mild autistic spectrum disorder or cognitive delay, and later trigger an epilepsy that aggravates the symptoms. In a vulnerable child, an autistic phenotype may result from the child's withdrawal reaction when an epileptic process interferes with a specific sensory or cognitive function (e.g. sound decoding system in verbal auditory agnosia) that is important for communication, even if the function is not directly related to the emotional and social behavioral processing systems.

In patients with autism that do not develop epileptic seizures, abnormal paroxysmal electroencephalographic activity can be seen in 7 to 28% of them. This percentage is even higher if the EEG is taken during sleep. Fifteen percent of the patients with autism receive antiepileptic medication, mostly because of epilepsy. There is no strong evidence that antiepileptic pharmacotherapy has any benefit in the autistic behavior.

The investigation of patients with autistic spectrum disorders, and particularly of those that develop language regression, should always include a good quality sleep encephalographic study in order to exclude acquired epileptic aphasia (Landau-Kleffner syndrome).

Key words: Autism, epilepsy, electroencephalogram, Landau-Kleffner syndrome.