A seizure is a brief episode of abnormal, excessive, synchronous, cerebral neuronal activity that results in an alteration of motor function, sensation, behavior, or consciousness. Epilepsy is a syndrome of recurrent seizures without an underlying etiology. Seizures occur more frequently in children and in the elderly. There is a 5%–10% incidence of seizure activity by the age of 80 and if you have a single seizure, your chance of having another is 40%–50%.
In 2010, the International League Against Epilepsy (ILAE) created a classification which describe seizures as being either “genetic”, “structural-metabolic”, or “unknown.” Genetic etiologies include channelopathies, progressive myoclonic epilepsies, malformations in cerebral cortical development, mitochondrial diseases, and neoplasms with suspected genetic contributions. Structural-metabolic etiologies include cerebrovascular disease, trauma, infections, neoplasms, and autoimmune/inflammatory processes. On a cellular level, the underlying etiology of a seizure can be attributed to loss of inhibitory gamma-aminobutyric acid (GABA) activity, abnormal voltage-gated calcium or sodium currents, and enhanced release of excitatory amino acids (glutamate).
Classifications of epilepsy that predated modern neuroimaging techniques used the terms “focal” and “generalized” to infer the presence or absence of a structural lesion. However, it is now acknowledged that “generalized” seizures on EEG can be the result of a focal etiology. For the most part, when seizures are secondary to a discrete, structural lesion, the term focal seizure is used. Focal (partial) seizures are described as simple, complex, or focal with secondary generalization. Complex focal seizures are not associated with impairment of consciousness. These often have automatisms. Automatisms are nonconsciously generated, repetitive movements such as lips smacking or chewing. A focal seizure evolving to a bilateral, convulsive seizure is termed a focal seizure with secondary generalization. Fifty-seven percent of all seizures are partial and a new onset, partial seizure suggests an underlying lesion.
Generalized seizures are symmetrical and synchronous, involving both cerebral hemispheres at onset. Generalized seizures often originate from deep, midline structures in the thalamus or brainstem. Loss of consciousness is noted at onset, typically without an aura. They represent 40% of all seizures and are further defined as tonic-clonic, myoclonic, clonic, atonic (astatic), tonic, or absence based on clinical manifestations and electroencephalographic findings. Generalized epileptic syndromes in children include infantile spasms (West syndrome), Lennox–Gastaut syndrome, childhood absence, juvenile myoclonic epilepsy, benign occipital epilepsy of childhood, Landau–Kleffner syndrome, and benign epilepsy with central temporal spikes. Febrile seizures are seen in 2%–5% of children between the ages of 6 months and 6 years.
While absence seizures last about 10 seconds without postictal confusion, most generalized seizures last less than 2–3 minutes and are associated with postictal fatigue and confusion. A seizure lasting longer than 5 minutes defines status epilepticus. Occasionally, partial or total focal paralysis (Todd’s) manifesting with transient focal weakness, aphasia, and hemianopsia can ...