Seizures: Types and Classification

by Roy Strowd, MD

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    00:01 So what are the types of seizures? Once we make the diagnosis, we've determined that the spell is indeed a seizure.

    00:07 Our first step is to figure out what type of seizure it is.

    00:10 And in general, we categorize seizures in two ways, as either partial and onset coming from a specific area out in the cortex, or generalized and onset and coming from a deep focus inside the brain.

    00:25 This terminology comes from a long history of evaluating seizures with surface EEG/electroencephalography on the surface of the brain.

    00:35 And when we hook the brain up to EEG we see out on the surface that those seizures that come from the cortex have an onset and we can see where the seizure begins.

    00:44 Here you can see in the green area, the seizure begins in the occipital lobe.

    00:48 Those EEG electrodes near the occipital lobe will show the seizure first, and then you can watch the seizures spread, either along the where pathway or the what pathway, those ingrained white matter tracks that help us understand what we're seeing.

    01:03 And that spread we see on the EEG for seizures that have a focal onset or focal onset seizures.

    01:10 In contrast, generalized seizures begin in a very deep focus, they still begin in a single area of the brain.

    01:18 But you can see here in this red deep focus in the midbrain that deep focus can't be seen on the surface EEG in a single location.

    01:27 The seizure starts deep in the brain, in the thalamus, and expands out through the internal capsule and the radiations from the thalamus in all directions equally.

    01:36 Shows up on the surface electrodes at the same time.

    01:40 And on the EEG, it looks like it just started all over the brain or had a generalized onset.

    01:46 At the end of the day, the seizure is always coming from a single focus.

    01:50 But we categorize seizures based on how they appear on the surface EEG as either focal onset or partial onset or generalized onset.

    02:00 And that's helpful because when we think about seizures, they have many different descriptions from patients.

    02:05 But we can categorize them, and as either focal or onset or generalized onset.

    02:12 And we'll learn that there are about 8 different seizure types that occur in patients and we can categorize all those clinical descriptions according to the 8 seizure types.

    02:23 There are 3 types of partial onset or focal onset seizures.

    02:27 A focal onset seizure starts in one area out on the surface of the brain in the cortex of the cerebrum.

    02:35 What's been historically called simple partial seizures are currently what's termed focal seizures with retained awareness begin in a specific area of the brain and are isolated and restricted only to that area of the brain.

    02:49 If the sensory cortex is involved, they present with sensory symptoms.

    02:53 If the motor cortex is involved, they present with isolated motor symptoms.

    02:57 Autonomic cortex, autonomic findings, and psychic areas or limbic areas of the brain have psychic auras, which are focal seizures with retained awareness, that's one seizure type.

    03:09 If a larger area of brain is involved, if a hemi area of brain one side of brain is involved in this seizure activity, we call those focal seizures with altered awareness or historically those were called complex partial seizures.

    03:24 Here the patient has altered awareness as either passed out or is unable to communicate or altered awareness in some way.

    03:32 Also with those sensory or motor phenomenon depending on where the seizure may occur.

    03:37 And then the third type of partial onset epilepsy is secondary generalized seizures.

    03:44 Those seizures may start in a focus, they may start with retained awareness, they may progress to altered awareness.

    03:50 But ultimately the entire brain becomes involved in the seizure and the patient will pass out and jerk and shake and sometimes have incontinence and lateral tongue biting.

    03:59 And those are secondarily generalized seizures, they started in a focus and then generalized.

    04:04 So those are the 3 types of focal onset or partial epilepsy.

    04:11 That's different from the generalized seizures that we see, these are seizures that have seizure activity that involves both hemispheres of the brain equally and symmetrically.

    04:20 And there are 5 types, 5 or 6 types of generalized seizures.

    04:26 Absence seizures are brief episodes, where the patient has loss of awareness or behavioral arrest.

    04:35 Tonic-clonic seizures, generalized seizures begin with tonic-clonic episodes or tonic-clonic motor activity.

    04:42 Myoclonic seizures are very brief single jerks, and myoclonic jerks are not always epileptic in origin as we go to sleep as we all go to sleep.

    04:52 Sometimes the body will jerk or have a myoclonic jerk and that's non-epileptic in origin.

    04:57 Myoclonic seizures have an epileptic origin but have that same myoclonic jerk.

    05:03 Clonic seizures are jerking, we can see tonic seizures with just the retain stiffening and atonic seizures.

    05:10 And each of these 6 types are generalized seizures.

    05:17 So let's walk through each of those seizure types.

    05:19 It's very important to understand what these looks like and how patients describe them.

    05:24 When a patient comes in with a seizure evaluation, we'll need to categorize the type of seizure.

    05:29 We said there are 3 types of focal onset seizure, there's what historically was called the simple partial seizures with retained consciousness.

    05:37 Patients may describe an abnormal smell or taste.

    05:40 These may present with staring spells, with retained consciousness, and patients have retained muscle tone during these events.

    05:50 If the seizure involves a larger area, historically, these were called complex partial seizures or focal epilepsy with loss of consciousness or altered awareness.

    05:59 They may be preceded by an aura and typically involves postictal confusion.

    06:04 And complex ictal automatisms.

    06:06 And these are automatic behaviors that occur automatically reflexively during the seizure, that may be lip smacking, it may be chewing, it may be a guttural sound, it may be swallowing and it's repetitive activity that is reflexive.

    06:20 And can frequently occur during these complex partial seizures or again, focal seizures with altered awareness.

    06:27 And then the last category was the secondary generalized seizures.

    06:29 These begin with an initial aura and then progress to involve convulsions.

    06:35 That progression has been termed a Jacksonian march.

    06:38 And classically, the Jacksonian March begins with motor activity in one limb that progresses up the limb more motor activity involving the entire limb and then generalizing throughout the body.

    06:49 Secondary generalized seizures are characterized by postictal confusion and sometimes a Todd's paralysis, and that's a weakness on one side of the body, the side opposite where the seizure began as a result of that postictal depression in brain activity.

    07:04 For the generalized seizures again, we said that there are absence types of generalized seizures.

    07:09 These are primary generalized and brief staring spells.

    07:13 They often can be confused by daydreaming, they're seen typically in children and associated with this 3 Hz spike-and-wave activity on the EEG.

    07:22 That's different from myoclonic generalized seizures.

    07:25 These are typically focal myoclonic jerks, brief periods of loss of consciousness but without convulsion and very little postictal confusion.

    07:33 They may be characterized just as a brief jerk.

    07:37 Tonic seizures or focal, isolated rigidity.

    07:40 Typically a period of time, a short period of seconds or minutes characterized by tonic activity, isolated rigidity of either one part of the body or the entire body.

    07:52 Atonic seizures are drop attacks.

    07:54 These are where patients lose postural tone.

    07:56 They're common in children, they're very difficult to control seizure and can result in severe injury.

    08:02 Patients will very suddenly lose all postural tone and fall to the ground.

    08:06 And many of these children wear a helmet or some other protective device because these seizures cannot be predicted and can result in severe injury to the child.

    08:16 And then generalized tonic-clonic seizures look very similar to the secondary generalized tonic-clonic seizures, but they don't have an aura.

    08:24 They don't have a clearly observed focal onset.

    08:28 Most often they do involve convulsion, but maybe non convulsive in patients with primary generalized epilepsy without aura.

    About the Lecture

    The lecture Seizures: Types and Classification by Roy Strowd, MD is from the course Seizures and Epilepsy.

    Included Quiz Questions

    1. Surface electroencephalography (EEG) will show a clearly identifiable starting point during focal seizures.
    2. Surface EEG will show the initial starting location of a generalized seizure.
    3. Focal onset seizures begin in the brainstem and travel outward.
    4. Generalized seizures usually only involve one hemisphere of the brain.
    5. Generalized seizures have a defined trajectory of depolarization on surface EEG.
    1. Secondary generalized seizure
    2. Absence seizure
    3. Myoclonic seizure
    4. Atonic seizure
    5. Tonic seizure
    1. Atonic seizures can result in fall injuries.
    2. Tonic-clonic seizures typically have an aura.
    3. Clonic seizures present as transient stiffness.
    4. Focal seizures always result in altered awareness.
    5. Todd’s paralysis is characterized by weakness on the same side of the body where the seizure began.
    1. Absence seizures show a “spike and wave” pattern on electroencephalography (EEG).
    2. A patient experiencing a strange taste or smell is likely having a generalized seizure.
    3. Jacksonian march refers to characteristic bilateral leg movements that resemble walking.
    4. Both secondary generalized seizures and tonic-clonic seizures will have an aura.
    5. Simple focal seizures result in lip-smacking or similar repetitive reflexive behaviors.

    Author of lecture Seizures: Types and Classification

     Roy Strowd, MD

    Roy Strowd, MD

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