Spike-and-wave
Spike-and-wave is a pattern of the electroencephalogram (EEG) typically observed during epileptic seizures. A spike-and-wave discharge is a regular, symmetrical, generalized EEG pattern seen particularly during absence epilepsy, also known as ‘petit mal’ epilepsy.[1] The basic mechanisms underlying these patterns are complex and involve part of the cerebral cortex, the thalamocortical network, and intrinsic neuronal mechanisms.[2]
The first spike-and-wave pattern was recorded in the early twentieth century by Hans Berger. Many aspects of the pattern are still being researched and discovered, and still many aspects are uncertain. The spike-and-wave pattern is most commonly researched in absence epilepsy, but is common in several epilepsies such as Lennox-Gastaut syndrome (LGS) and Ohtahara syndrome. Antiepileptic drugs (AEDs) are commonly prescribed to treat epileptic seizures, and new ones are being discovered with fewer adverse effects. Today, most of the research is focused on the origin of the generalized bilateral spike-and-wave discharge. One proposal suggests that a thalamocortical (TC) loop is involved in the initiation spike-and-wave oscillations. Although there are several theories, the use of animal models has provided new insight on spike-and-wave discharge in humans.[3]
History[edit]
History of generalized epilepsy with absence seizures are dated to the eighteenth century, however the inventor of the electroencephalogram (EEG), Hans Berger, recorded the first EEG of an absence seizure in the 1920s, which led the way for the general notion of spike-and-wave electrophysiology. His first recording of a human EEG was made in 1924 using a galvanometer, but his results were very crude and showed small, undefined oscillations. He continued to refine his technique and increase the sensitivity to the galvanometer, in which he accumulated many EEGs of individuals with and without a brain malfunction or disorder. Among those tested were patients with epilepsy, dementia, and brain tumors.[4] Hans Berger published his findings in 1933, however his results did not give a definitive characterization of the general EEG pattern seen during an epileptic seizure. In 1935, F.A. Gibbs, H. Davis, and W.G. Lennox provided a clear description of EEG spike-and-wave patterns during a petit mal epileptic seizure.[5] An intracellular recording performed by DA Pollen in 1964 revealed that the "spike" aspect of the phenomenon was associated with neuronal firing and the "wave" aspect was associated with hyperpolarization.[6]
Spike-and-wave in epilepsy[edit]
Absence epilepsy[edit]
Bursts of generalized spike-and-wave discharges lasting two seconds or longer is considered an absence seizure.[20] Absence seizures are generalized epileptic seizures that can be divided into two types, typical and atypical. Typical and atypical absence seizures display two different kinds of spike-and-wave patterns. Typical absence seizures are described by generalized spike-and-wave patterns on an EEG with a discharge of 2.5 Hz or greater. They can be characterized by an increase in synchronization of discharges in the thalamocortical circuitry. They can also be characterized by the acute onset and termination of the seizure. Atypical absence seizures have a higher frequency in children with severe epilepsy that suffer from multiple types of seizures. The spike-and-wave pattern seen here is more irregular than the generalized pattern and also seems to be slower. This irregular pattern is due to non-synchronous discharges of the thalamocortical circuitry. The onset and termination in these atypical absence seizures seem to be less acute than the typical absence seizures.[21]
Lennox-Gastaut syndrome[edit]
Epileptic encephalopathies are a group of conditions that result in deterioration of sensory, cognitive, and motor functions due to consistent epileptic activity. Lennox-Gastaut syndrome (LGS) is a childhood epileptic encephalopathy characterized with generalized seizures and slow spike-wave activity while awake. LGS is a combination of atonic absences, tonic seizures, cognitive deterioration, and slow spike-wave activity in the EEG. This syndrome usually results from focal, multifocal, or diffuse brain damage and can be divided into symptomatic and cryptogenic types. Cognitive deterioration with high-frequency spike-wave activity affects most patients 2–9 years old with generalized seizures. The age of onset for LGS is between 1 and 10 years, between 2 and 6 years for symptomatic cases and 5 and 8 years for cryptogenic cases. Episodes can be triggered by modifications of treatment, which usually involves benzodiazepines, or changes in the conditions of life.[22]
Ohtahara syndrome[edit]
Ohtahara syndrome (OS), also known as early infantile epileptic encephalopathy (EIEE) with suppression-burst (S-B), is the most severe and the earliest-developing epileptic encephalopathy in children. This syndrome is characterized on an EEG by high voltage bursts and slow waves mixed with multifocal spikes alternating with almost flat suppression phases. The S-B will gradually begin to taper away at 3 months and disappear by 6 months. OS will transition to West syndrome or LGS with age. Tonic spasms are the main seizures observed in OS. Unlike LGS, the spike-and-wave pattern is consistent during both waking and sleeping states.[23] Symptoms of OS include:[24]