Epilepsy is defined by the occurrence of at least two unprovoked seizures with or without convulsions (i.e., violent, involuntary contraction[s] of the voluntary muscles) separated by at least 24 hours, often with neurobiological, cognitive, psychological, and social consequences. A seizure results from an excessive discharge of cortical neurons and is characterised by changes in electrical activity as measured by the electroencephalogram (EEG).
WHAT ARE THE CAUSES OF EPILEPSY?
Seizures result from excessive excitation or disordered inhibition of neurons. Initially, a small number of neurons fire abnormally. Normal membrane conductances and inhibitory synaptic currents then break down, and excitability spreads locally (focal seizure) or more widely (generalised seizure). Epileptic seizures result only when there is also synchronisation of excessive neuronal firing.
Mechanisms that may contribute to synchronous hyperexcitability include (1) alterations of ion channels in neuronal membranes, (2) biochemical modifications of receptors, (3) modulation of second messaging systems and gene expression, (4) changes in extracellular ion concentrations, (5) alterations in vesicle trafficking and neurotransmitter release, (6) alterations in neurotransmitter uptake and metabolism, and (7) modification in the ratio and function of inhibitory circuits.
WHAT ARE THE SIGNS AND SYMPTOMS OF EPILEPSY?
Table 1–1 shows the International League Against Epilepsy (ILAE) the classification of electroclinical syndromes and other epilepsies. Figure 1–1 shows the ILAE terminology for the classification of seizures.
FIGURE 1–1. 2010 ILAE revised terminology for the classification of seizures.
Many patients, particularly those with focal onset seizures with dyscognitive features or generalised tonic-clonic (GTC) seizures, are amnestic to the actual seizure event.
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