The typical seizures seen in LGS usually begin at age 3 years, typically between age 1 and 7 years. Most people with LGS have daily seizures. Due to the high seizure frequency, it can be difficult to tell what kind of seizures a person is having. Video-EEG monitoring may help classify each seizure type. Correct classification of seizures is important to choose the therapies that are most likely to help people with LGS. Below are descriptions of the common seizure types.
Tonic seizures are the most common and characteristic type, and form the core of the syndrome.
- Tonic seizures consist of a sustained increase in muscle contraction lasting a few seconds to minutes (resulting in stiff extremities). These may be limited to a slight bent of the body at the neck and waist with a brief interruption of breathing due to stiffening of muscles used for breathing. Stronger seizures may have facial grimacing and stiffening and slow raising of the arms.
- Tonic seizures may result in a fall if they occur when the person is awake.
- Tonic seizures occur more often in sleep.
- Tonic seizures may not be present at the onset of LGS, or may be missed if a sleep EEG is not obtained. Some events in sleep may be subtle, with only a slow movement of the eyes upward and tensing of the muscles of the chest or abdomen (associated with a specific EEG change).
- The presence of tonic seizures is associated with a poor prognosis for development.
- Repeated or clusters of tonic seizures and atypical absence seizures can lead to non-convulsive status epilepticus.This can be a common problem.
- Tonic seizures last from a few seconds to a minute. Longer ones can have tremors or look like vibrations of part or all of the body.
Atypical absence seizures are the second most common seizure type associated with LGS.
- This seizure is represented by a brief loss or lapse of awareness (usually seconds, 15-30). This seizure type is difficult to identify because of its gradual onset and ending. In a child or adult with developmental delay that already affects their responsiveness. It may be hard to tell if the child is not responding because of an absence seizure or their development and intellectual problems.
- Typically, the person can not tell the parent or caregiver that they are experiencing an interruption in their awareness. The caregiver may think they are inattentive, daydreaming or simply still for the moment. Yet, tThe EEG shows a characteristic slow-spike and wave pattern during these events.
- Complex partial seizures my also occur in LGS and present with staring episodes. Complex partial seizures may be confused with atypical absence seizures. A video-EEG to capture a typical event can help tell if the staring episode is indeed a seizure, and, if so, what type.
Atonic Seizures or Drop Attacks
Drop attacks occur in slightly over half of the people with LGS. These seizures result in repeated falls, causing injury to the face and head. These seizures should be the primary factor to consider when making treatment decisions.
- Atonic seizures are characterized by a sudden loss of postural muscle tone causing a rapid fall to the ground (if walking) or collapse at the waist (falling forward or backwards if sitting). It may look like the person went suddenly limp, with no effort made to catch or protect themselves. These last only a few seconds, and the person usually recovers immediately after the fall. Sometimes, these are limited to the head, resulting in head drop or nods only.
- Many atonic seizures are associated with an initial myoclonic component (myoclonic-atonic seizure). The myoclonic component is recognized by the sudden shock-like, jerk of the body. This lasts only a fraction of a second. However, myoclonic-atonic seizures may be seen in other epilepsy syndromes, such as Doose Syndrome, that do not necessarily progress to LGS. As a result, the presence of drop attacks does not confirm the diagnosis of LGS.
Other Seizure Types
In addition to the common seizure types described above, other seizure types are common. Some may occur more frequently in adolescents and adults, or occasionally before the characteristic seizure types. Partial onset seizures with or without secondary generalization, generalized tonic-clonic seizures and one-sided clonic seizures are common.
- Partial-onset seizures may be characterized by staring with a slow decrease in muscle tone (slump) and unresponsiveness, lasting 30 to 60 seconds. These may progress to a full body, convulsive seizure (generalized tonic-clonic) with an initial brief stiff phase (tonic), followed by jerking in both arms and legs (usually more in the arms) (clonic phase) with bluish discoloration around the mouth. The convulsive phase typically lasts from 45 to 90 seconds.
- The seizure may begin as a generalized tonic-clonic event, without the prior partial phase, and if it does, is more dangerous to the patient, as there is no warning and may result in a fall with injury.
- As the child reaches adolescent or early adult years the seizure types may change into more complex partial and generalized tonic-clonic, however, the tonic seizures occurring in sleep typically persist into adulthood.
Most patients with LGS will have one or several episodes of status epilepticus (a series of seizures, without return to the child’s normal state, lasting 30 minutes or longer). This may consist of a mixture of atypical absence, tonic and other seizure types. These seizures often take days to weeks for the child to recover from and likely contribute to the progressive intellectual decline.
- Every patient with LGS should have an emergency treatment plan that is tailored to their seizures and access to emergent medical care. This should be reviewed periodically with the family and communicated to their primary care physician.
Interictal (Between Seizures)
The background activity when a person is awake is often slow for the patient’s age. This can be constant or transient. Permanent slowing has been associated with a poorer cognitive or developmental prognosis. Normal sleep architecture and patterns may not be recognizable due to the frequent seizure-like discharges.
- The classic EEG feature of LGS is a slow spike-wave complex, seen on both sides or over the entire head, repeating at 1-2 per second. The same pattern may be seen during an atypical absence seizure. The frequent presence of the slow spike-wave complexes and the waxing and waning presence can make it difficult to distinguish between the interictal (between seizure) and ictal (during seizure) pattern.
- The slow spike-wave complexes may not be present when the child is first diagnosed with seizures, and only becomes apparent on a subsequent EEG, making the initial diagnosis difficult in some children. The occurrence of slow spike-wave complexes may decrease in adolescents and adults.
- In patients whose seizure frequency decreases, the pattern can change to single spike-and-wave complexes during sleep and then their subsequent disappearance. Focal spike (epileptiform discharges) or focal slowing may be seen. Bursts of generalized polyspikes at 10 per second or more are seen frequently enough to be considered an additional criterion for LGS. These are seen best in sleep, and may be associated with a nocturnal tonic seizure (as the ictal pattern).
- As children reach early adult years, only 30% to 50% still have the characteristic EEG and clinical characteristics.
Ictal (During Seizures)
- The EEG during a tonic seizure reveals generalized, fast (10-15 per second), low-amplitude activity, seen best over the anterior head regions. This slows in frequency and increases in amplitude as the seizure progresses. This may be preceded by a single generalized spike-and-wave complex. The clinical features typically begin within one second of the EEG manifestations.
- Diffuse, slow (less than 2 – 2.5 per second), spike-and-wave complexes characterize the EEG during an atypical absence seizure. This may be difficult to distinguish from the interictal bursts.
- Atonic, myoclonic and myoclonic-atonic seizures have an EEG characterized by bilateral slow spike-and-wave complexes, polyspike-and-wave complexes or rapid polyspikes.