(Click on links below to see video examples)
We try to classify seizures for several reasons. Most importantly is to be able to provide a common framework for communication. A classification scheme also helps the doctor place the disease into categories, which relay consistent, relevant information to aid in the diagnosis and treatment of epilepsy.
In Veterinary Medicine, seizures are commonly classified by two methods:
1. Descriptive or phenomenological: With this form of classification, we use descriptive terms (semiology) to define the seizure type. There are 3 basic seizure types and many subtypes.
Generalized: Formerly Grand mal
- Tonic/Clonic: A sequence consisting of a tonic (muscle contraction or stiffening) followed by a clonic (repeated jerking) phase.
- Tonic: sustained increase in muscle contraction (stiffening), lasting a few seconds to minutes. Extensor or flexor rigidity.
- Clonic: repeated jerking or myoclonus, which is regularly, repetitive involving the same muscle groups usually prolonged at a frequency of 2–3 cycles/second.
- Absence: Recognized as a brief (usually less than 20 sec.) generalized seizure with impaired consciousness and specific EEG changes characterized by spike-and-slow-wave complexes, which are bilaterally represented in the cerebral hemispheres.
- Typical: For a video example, go to: http://www.chihuahuaclubofamerica.com/idiopathic-epilepsy/epileptic-seizures-in-chihuahuas
- Atypical: More pronounced changes in tone. An onset or cessation that is not as abrupt and has EEG changes that dissimilar.
- Absence with special features: Typically has features of rapid, involuntary, disorganized contractions of individual muscle groups (myoclonia) and in humans may involve myoclonia of the eyelids with sensitivity to light.
- Atonic: sudden loss or weakness of muscle tone without an apparent preceding myoclonic or tonic event lasting ≥ 1-2 seconds involving head, trunk or limb musculature.
- Myoclonic: Myoclonus (sudden brief, single or multiple contraction(s) of muscle(s) or muscle groups). Can be of variable areas (i.e. body, or limb).
- Myoclonic (regular and repetitive jerking)
- Myoclonic atonic (regular and repetitive jerking, followed by a sudden loss of muscle strength and a fall - atonic)
- Myoclonic tonic (regular and repetitive jerking, followed by a sudden increase of muscle tone - stiffening)
Focal: Formerly Petit mal
- With cognition: implies an “awareness” of surroundings
- Typically, responsive to verbal cues but may have an “affective” state described as panicked, fearful or anxious.
- With dyscognition: implies an “unawareness” of surroundings
- Typically, “unresponsive” to verbal cues
- There is insufficient evidence to characterize as Generalized, focal, or both.
2. Cause or Etiological: With this form of classification, the cause of the seizure determines which group it falls in. Generally speaking, this form of classification may help a little with treatment and prognosis but it can often lead to inappropriate treatment choices. We try to avoid this type of labeling. Examples of causes of seizures may include:
- Genetic defect
- Brain tumor
- Head trauma
- Congenital malformation
- Infection or inflammation of the brain (encephalitis)
- Toxin or poisoning
- Metabolic causes (liver failure, etc...)
3. Syndromic: This is the most useful form of classification when a specific cause is not known. If we can group the patient into a syndrome based on certain factors such as age when the seizures first started, length of time since the seizures started, presence of abnormalities in between the seizures (and many others), we can make important decisions regarding diagnostic tests to run, treatment and prognosis. There are four basic syndromes:
A demonstrated pedigree showing direct or indirect modes of inheritance. A strong suspicion of a genetic basis. Often a diagnosis by excluding other causes. May also be referred to as Primary or Idiopathic epilepsy.
- Generally, seizures start between 1-5 years old (range months to 10 years).
- Generally, a normal neurological exam between seizures
- Progression over time = Static.
Metabolic or Reactive
Epileptic seizures secondary to a systemic disorder or toxin.
- Generally, patients are “sick”.
- Generally, if the cause is removed, the seizures stop.
- Progression over time = Variable depending on sickness.
Structural: a known or suspected primary damage or disorder of the brain.
- Static: Does not progress over time. Example; congenital malformation, head trauma, stroke, etc.
- Progressive: Progresses over time demonstrated by the development of clinical signs attributed to brain dysfunction independent of the seizures (e.g. blindness, balance problems, behavior changes, etc.). Example; Neoplasia, encephalitis, degenerative disease, etc.
Unknown: the cause is unknown and might be genetic, metabolic/reactive or structural.
- Typically, enough data is not available to classify.
- No cause can be found in a patient who is classified as either Metabolic/Reactive or Structural and the clinical course does not behave in an expected manner.