Epilepsy is defined by the occurrence of at least two unprovoked seizures with or without convulsions (ie, 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 characterized by changes in electrical activity as measured by the electroencephalogram (EEG).
Seizures result from excessive excitation or from 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 (generalized seizure). Epileptic seizures result only when there is also synchronization 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.
Table 53–1 shows the International League Against Epilepsy (ILAE) classification of electroclinical syndromes and other epilepsies. Figure 53–1 shows the ILAE terminology for classification of seizures.
Many patients, particularly those with focal onset seizures with dyscognitive features or generalized tonic-clonic (GTC) seizures, are amnestic to the actual seizure event.
2010 ILAE revised terminology for classification of seizures.
TABLE 53–12010 ILAE Electroclinical Syndromes and Other Epilepsies |Favorite Table|Download (.pdf) TABLE 53–1 2010 ILAE Electroclinical Syndromes and Other Epilepsies
Electroclinical Syndromes (and common examples arranged by age at onset)
Juvenile Myoclonic Epilepsy (JME)
Progressive Myoclonic Epilepsy (PME—including Lafora)
Epilepsy with Generalized Tonic-Clonic Seizures Alone
Distinctive Constellations (and common example):
Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis
Epilepsies Attributed to and Organized by Structural-Metabolic Causes (and common examples):
Malformations of Cortical Development
Epilepsies of Unknown Cause
Symptoms depend on seizure type and where the abnormal firing occurs. Although seizures can vary between patients, they tend to be stereotyped within an individual.
Focal seizures (ie, partial seizures) begin in one hemisphere of the brain, and unless they become secondarily generalized (ie, evolve to a bilateral convulsive seizure), result in an asymmetric seizure. Focal seizures manifest as alterations in motor functions (eg, twitching or shaking), sensory (eg, numbness or tingling) or somatosensory symptoms, aberrations in behavior, or automatisms. Focal seizures without dyscognitive features (formerly called simple partial seizures) are associated with no impairment of consciousness. In focal seizures with dyscognitive ...
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