Absence seizures
| Absence seizure | |
|---|---|
| Classification and external resources | |
| Specialty | Neurology |
| ICD-10 | G40.3 |
| ICD-9-CM | 345.0 |
| DiseasesDB | 32994 |
| MedlinePlus | 000696 |
| eMedicine | neuro/3 |
| MeSH | D004832 |
Absence seizures are one of several kinds of seizures. These seizures are sometimes referred to as petit mal seizures (from the French for "little illness", a term dating from the late 18th century). Absence seizures are characterized by a brief loss and return of consciousness, generally not followed by a period of lethargy (without a notable postictal state).
The clinical manifestations of absence seizures vary significantly among patients. Impairment of consciousness is the essential symptom, and may be the only clinical symptom, but this can be combined with other manifestations. The hallmark of the absence seizures is abrupt and sudden-onset impairment of consciousness, interruption of ongoing activities, a blank stare, possibly a brief upward rotation of the eyes. If the patient is speaking, speech is slowed or interrupted; if walking, they stand transfixed; if eating, the food will stop on its way to the mouth. Usually, the patient will be unresponsive when addressed. In some cases, attacks are aborted when the patient is called. The attack lasts from a few seconds to half a minute, and evaporates as rapidly as it commenced. Absence seizures generally are not followed by a period of disorientation or lethargy (post-ictal state), in contrast to the majority of seizure disorders.
Mixed forms of absence frequently occur. These seizures can happen a few times a day or in some cases hundreds of times a day, to the point that the person cannot concentrate in school or in other situations requiring sustained, concentrated attention.
Typical absences are easily induced by hyperventilation in more than 90% of people with typical absences. This is a reliable test for the diagnosis of absence seizures: a patient suspected of typical absences should be asked to overbreathe for 3 minutes, counting their breaths. Intermittent photic stimulation may precipitate or facilitate absence seizures; eyelid myoclonia is a common clinical feature.
A specific mechanism difference exists in absence seizures in that T-type Ca++ channels are believed to be involved. Ethosuximide is specific for these channels and thus it is not effective for treating other types of seizure. Valproate and gabapentin (among others) have multiple mechanisms of action including blockade of T-type Ca++ channels and are useful in treating multiple seizure types. Gabapentin can aggravate absence seizures.
The primary diagnostic test for absence seizures is EEG. However, brain scans such as by an MRI can help rule out other diseases, such as a stroke or a brain tumor.
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