First Published Tuesday, 2 June 2009
by Richard E Frye MD PhD
Autism is associated with a high prevalence of both clinical and subclinical seizures and epilepsy. It is important to understand the distinction between clinical seizures, subclinical seizures, and epilepsy.
A clinical seizure occurs when abnormal rhythmic electrical discharges in the brain result in abrupt characteristic motor behaviour usually associated with loss of consciousness. Most people think of generalised tonic-clonic seizures when they think of a seizure occurring. During a generalised seizure, a person loses consciousness and both arms and legs move synchronously either in a repetitive jerking fashion or become stiff. Most generalised seizures only last a few minutes and will not result in long term damage, but seizures that go on for ten minutes or more can be dangerous to a person and require intervention. Most parents who have children with epilepsy have a medication such as DiastatTM that can be used to stop the seizure if it continues on for a prolonged period of time. Some people have partial seizures. These types of seizures are limited to abnormal rhythmic movements on one side or one portion of the body, for example the arm or the face. When these types of seizures are associated with a change in consciousness, they are known as partial complex seizures. Still another type of seizure is a myoclonic seizure which can be localised or generalised. Many other types of seizures exist and many other abnormal movements such as tics and movement disorders can be mistaken for seizures, so it is important for a medical professional to evaluate anyone suspected of having seizures.
Epilepsy is defined by more than one unprovoked seizure. Many children will have febrile seizures. Since the fever provoked the seizure, by definition, children with febrile seizures do not have epilepsy. Many typically developing children also will have more than one unprovoked seizure and be diagnosed with epilepsy. The epilepsy will resolve in most of these children in one or two years.
Autism is associated with an increased risk of epilepsy and almost every type of seizure has been described in autism. There appears to be two age peaks when epilepsy presents itself in autism: before five years of age and in adolescence. The risk of epilepsy in autism increases with severe mental retardation and/or cerebral palsy. Several genetic syndromes associated with autism, such as Rett’s, fragile X, and Angelman syndrome and tuberous sclerosis, are associated with a particularly high rate of epilepsy. Thus, the underlying aetiology, if known, can be very helpful for predicting whether an individual with autism will develop epilepsy.
Autistic children have a high prevalence of subclinical epileptiform discharges. These rhythmic electrical disturbances in the brain do not manifest themselves as a typical clinical seizure (as described above), but may disrupt cognitive development. Some individuals may have subtle signs of subclinical seizures such as periodic episodes of unresponsiveness in which they stare into space, but others will not have any other symptoms aside from atypical cognitive development.
When these subclinical discharges affect development, the seizure syndrome can be called an epileptic encephalopathy. Two of the best studied epileptic encephalopathy syndromes are Landau-Kleffner syndrome and continuous spike waves during slow-wave sleep (CSWS). Both of these syndromes are characterised by continuous rhythmic discharges occurring during sleep. Children with these syndromes undergo sudden or gradual regression in language usually after three years of age and manifest behavioural symptoms that include hyperactivity, aggressiveness and depression. However, we are starting to recognise that other non-classic epileptic encephalopathies also exist. Recently, we have reviewed a series of children with subclinical epileptiform discharges and atypical development who were treated at our facility. We found that over half of these children presented with a language disorder, attention problems and mild autism symptomatology and most children did not have any overt signs of seizures or a history of language regression. Importantly, the majority of these children improved with antiepileptic treatment.
Most of the time, epilepsy is a treatable disorder. The mainstay for treatment is antiepileptic medication; however, sometimes epilepsy does not respond to antiepileptic medication. Sometimes epilepsy appears to respond to immunomodulatory therapies such as steroids and intravenous immunoglobulin (IVIG). Other treatments, such as the ketogenic diet, can also be used to treat epilepsy. Surgery is sometimes considered for epilepsy that does not respond to other therapies. A small part of the brain can be removed if the epilepsy arises from a small silent part of the brain. Other procedures, such as multiple subpial transection (MST), can be used if the seizures arise from an eloquent part of the brain that is involved in language processing or another critical cognitive operation.
Autistic children are at increased risk of being diagnosed with epilepsy, but epilepsy is usually a treatable condition. As long as seizures are controlled, epilepsy should not have a major adverse impact upon a child’s life. Some autistic children could have an epileptiform encephalopathy that may respond to standard treatment for epilepsy, particularly if their symptoms of autism are mild. Interestingly, many of the treatments for epilepsy overlap those used for autism.
Source: The Autism File Issue 31 2009
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