A seizure represents a temporary disruption of the brain’s normal electrical activity. This sudden surge of uncontrolled electrical signals can affect movement, sensation, behavior, and awareness. While some seizures might be barely noticeable, others involve significant physical changes. The specific symptoms observed during a seizure depend on the brain regions involved in this abnormal electrical firing.
Understanding Seizure Classification
Medical professionals categorize seizures primarily based on where they originate in the brain. The three main categories of seizure onset are focal, generalized, and unknown onset.
Beyond the origin, seizures are further characterized by the person’s level of awareness during the event, indicating whether consciousness is maintained or impaired. Classification also considers the presence of motor symptoms (like movements or convulsions) or non-motor symptoms (like staring spells or changes in sensation).
Focal Seizures
Focal seizures begin in one specific area or group of cells within one side of the brain. These seizures can present in diverse ways, reflecting the specialized functions of different brain areas.
Focal Onset Aware Seizures
During a focal onset aware seizure, the person remains fully conscious and aware of their surroundings throughout the event. Despite this awareness, they may experience involuntary physical sensations or movements, such as localized muscle jerking, tingling, or numbness in a specific body part.
Sensory changes are common, including unusual smells or tastes, flashing lights, or shifts in emotion like fear or joy, or a strange wave-like sensation. These seizures typically last less than two minutes, and the person usually remembers the event clearly afterward.
Focal Onset Impaired Awareness Seizures
Focal onset impaired awareness seizures involve a change or loss of awareness during the event. The person may appear confused, dazed, or unresponsive to their environment. They may not remember what happened during the seizure.
These seizures often involve automatisms, which are repetitive, involuntary movements. Common automatisms include lip-smacking, chewing, fumbling with clothes, or repeating words or phrases. The duration of these seizures is typically between 30 seconds and three minutes, and confusion may persist for a period afterward.
Generalized Seizures
Generalized seizures involve abnormal electrical activity that affects both sides of the brain from the very beginning of the event. These seizures often result in a loss of consciousness and can manifest with a variety of motor or non-motor symptoms.
Tonic-Clonic Seizures
Tonic-clonic seizures consist of two distinct phases: the tonic phase and the clonic phase. The tonic phase involves a sudden stiffening of the muscles, causing the person to lose consciousness.
This stiffening is typically followed by the clonic phase, characterized by rhythmic jerking movements of the arms and legs. During this phase, individuals may also experience loss of bladder or bowel control and may bite their tongue. The entire seizure usually lasts between one and three minutes, after which the person may feel confused or tired.
Absence Seizures
Absence seizures are characterized by brief, sudden lapses of consciousness. The person might appear to be staring blankly into space. These seizures are more common in children.
During an absence seizure, subtle movements such as lip smacking, eyelid fluttering, or small hand gestures might occur. The seizure typically lasts less than 10 to 20 seconds, and the person quickly returns to full awareness afterward with no memory of the event.
Myoclonic Seizures
Myoclonic seizures involve sudden, brief, shock-like jerks or twitches of a muscle. These rapid contractions can affect one part of the body or be more generalized.
These seizures are usually very short, often lasting less than a second or two, and can occur in clusters. Typically, awareness is preserved during a myoclonic seizure, and the person can continue their activity immediately afterward.
Atonic Seizures
Atonic seizures, also known as “drop attacks” or “drop seizures,” cause a sudden and complete loss of muscle tone. This abrupt limpness can lead to a person’s head dropping, objects being dropped from their hands, or a sudden fall to the ground.
Despite the sudden loss of muscle control, the person often remains conscious during the seizure. These seizures are typically brief, lasting less than 15 seconds.
Tonic Seizures
Tonic seizures are characterized by a sudden and sustained stiffening or tension in the muscles. This stiffening often affects the muscles of the arms, legs, or trunk. This sudden rigidity can cause them to fall.
These seizures typically last around 20 seconds and are more likely to occur during sleep. Following a tonic seizure, a person may experience temporary confusion or fatigue.
Clonic Seizures
Clonic seizures involve rhythmic, jerking movements of the muscles. These movements are repetitive and can affect one or both sides of the body. Unlike myoclonic jerks, the movements in clonic seizures are more regular and sustained. Clonic seizures are relatively rare and are most commonly observed in infants.
Unknown Onset Seizures
The category of unknown onset seizures is used when the beginning of a seizure cannot be determined. This classification applies when the seizure is not witnessed, such as when it occurs during sleep or if the person is alone.
Over time, as more information becomes available, seizures initially classified as unknown onset may be reclassified. They might eventually be identified as either focal or generalized seizures once sufficient evidence regarding their origin is gathered.