Generalized-Onset Seizures and Unclassified Seizures

Generalized-onset seizures are the most common type in young children. These seizures are classified as primary or generalized when clinical signs, symptoms, and supporting EEG changes indicate involvement of both hemispheres at onset. The clinical symptoms include unconsciousness and involve varying bilateral degrees of symmetric motor responses without evidence of localization to one hemisphere.

These seizures are divided into four broad categories:

• Absence Seizures - Absence seizures are generalized, non-convulsive epileptic events and are expressed mainly as disturbance in consciousness. Formerly referred to as petit mal seizures, absence seizures typically occur only in children and cease in adulthood or evolve to generalized motor seizures. Although typical absence seizures have been characterized as a blank stare, motionless, and unresponsiveness, motion occurs in many cases of absence seizures. This motion takes the form of automatism such as lip smacking, mild clonic motion (usually in the eyelids), increase or decrease postural tone, and autonomic phenomena . There often is a brief loss of contact with the environment. The seizures usually last only a few seconds, and then the person is able to resume normal activity immediately. Atypical absence seizures are similar to typical absence seizures except for greater alterations in muscle tone and less abrupt onset and cessation. In practice, it is difficult to distinguish typical from atypical absence seizures without benefit of supporting EEG findings.
• Atonic Seizures - In akinetic or atonic seizures, there is a sudden, split-second loss of muscle tone leading to slackening of the jaw, drooping of the limbs, or falling to the ground. These seizures are also known as drop attacks.
• Myoclonic Seizures - Myoclonic seizures involve brief involuntary muscle contractions induced by stimuli of cerebral origin. A myoclonic seizures involve bilateral jerking of muscles, generalized or confined to the face, trunk, or one or more extremities. Tonic seizures are characterized by a rigid, violent contraction of the muscles, fixing the limbs in a strained position. Clonic seizures consist of repeated contractions and relaxations of the major muscle groups.
• Toni-Clonic Seizures - Tonic-clonic seizures, formerly called grand mal seizures, are the most common major motor seizure. Frequently, a person has a vague warning (probably a simple partial seizure) and experiences a sharp tonic contraction of the muscles with extension of the extremities and immediate loss of consciousness. Incontinence of bladder and bowel is common. Cyanosis may occur from contraction of airway and respiratory muscles. The tonic phase is followed by the clonic phase, which involves rhythmic bilateral contraction and relaxation of the extremities. At the end of the clonic phase, the person remains unconscious until the RAS begins to function again. This is called the postictal phase. The tonic-clonic phases last approximately 60 to 90 seconds.

Unclassified Seizures

Unclassified seizures are those that cannot be placed in one of the previous categories. These seizures are observed in the neonatal and infancy periods. Determination of whether the seizure is focal or generalized is not possible. Unclassified seizures are difficult to control with medication.