Epilepsy and Developmental Disability Part I : Developmental Disorders in Which Epilepsy May be Comorbid

Epilepsy is common in patients with developmental disability. The approaches used to diagnose and treat patients with developmental delay and epilepsy may differ from those used for other patients and require additional special attention. This article reviews developmental disorders in which epilepsy is comorbid and treatment strategies that are used for patients that present with both disorders. It outlines the value of pharmacological and surgical treatments depending on the individual patient, and highlights the need for monitoring nutritional status. The importance of collaboration and cooperation from an interdisciplinary team to enhance functioning and to achieve optimal quality of care for the patient is discussed. In addition to the current knowledge and practices regarding medical treatment for patients with epilepsy and developmental disorders, this article indicates what is currently not known and what needs further research and documentation. Unusual terms used in this article are explained in a glossary. Epilepsy is a chronic neurological condition characterized by recurrent seizures that are caused by abnormal neuronal activity. Epilepsy can be classified as either idiopathic or symptomatic. Idiopathic epilepsy has no known cause, and the patient has no other signs of neurological disease or intellectual deficiency. Symptomatic epilepsy results from a known condition, such as neoplasms, vascular anomalies, scars, stroke, genetic factors, birth trauma, brain injury, or poisoning (Engel, 1998). Epilepsy affects approximately 1% of the general population at any time. Approximately 10% of the general population will experience a seizure in their lifetime and 3% will develop epilepsy by the age of 75. Many patients with developmental disorders present with an epilepsy comorbidity. For example, seizures appear in more than 20% of children with cerebral palsy, unspecified cognitive impairment, pervasive developmental delay, as well as in specific genetic syndromes associated with cognitive impairment. In addition, there are different types of epilepsy that may be associated with different types of developmental disability. Both the paper electroencephalogram (EEG) and the video EEG remain the most valuable tools that are used to evaluate patients with both epilepsy and a developmental disorder. The approaches used to diagnose and treat patients with developmental delay and epilepsy may differ from other patients and require additional special attention (Mattson, 1996; Steffenburg, Hagberg & Kyllerman, 1996). While the focus of this paper is on epilepsy in people with a primary developmental disorder, the companion paper, Part II, outlines what is known about the developmental consequences of seizures in neurocognitive and neurobehavioural development. The Molecular Basis of Epilepsy Inhibition versus excitation hypotheses The most predominant hypotheses of mechanisms of epileptogenesis implicate the amino acid transmitters gamma aminobutyric acid (GABA) and glutamate. GABA is thought to be the main neurotransmitter at inhibitory neurons, while glutamate is thought to be the main neurotransmitter at the excitatory synapses (Snead, 1995). Normal brain function depends upon a balance of both excitation and inhibition. If there is an imbalance of either excitation or inhibition in the brain, seizure production may result. If excitation exceeds inhibition, the brain tissue becomes hyperexcitable leading to a low seizure threshold. If the imbalance is sufficiently large, a seizure occurs and may eventually lead to epilepsy recurring, spontaneous seizures. Research is currently being done to investigate the hypotheses that chronic low seizure threshold results either from too much activity in the excitatory glutamatergic system (the glutamate hypothesis) or from too little activity in the inhibitory GABA system (GABA hypothesis). Thus far, neither hypothesis has been conclusively proven; however, there is pharmacological evidence to support both hypotheses (Burnham, 1998). PERSAD, THOMPSON, AND PERCY 124