The form, intensity, and duration of seizures are related to the number and type of brain cells affected. There are two broad types of seizures: generalized and focal. They range from convulsions to momentary lapses of attention.

When both hemispheres (sides) of the brain are involved, the seizures are termed “generalized” and affect consciousness and motor function from the onset. When only one hemisphere (side) of the brain is affected, the seizures are called “focal” and initially have specific effects depending on the part of brain involved. Persons can experience both seizure types.

 

Types of Seizures

GENERALIZED SEIZURES – involving both hemispheres of the brain

Tonic-Clonic Seizure (formerly known as “Grand Mal”)

A tonic-clonic seizure is characterized by a convulsion in which the person’s body stiffens, arms flex, legs, head and neck extend, and the jaws clamp shut; this is the “tonic” phase. The person falls to the ground, sometimes uttering a hoarse cry, and temporarily loses consciousness for a few minutes. During this time, breathing appears difficult or stops, the body jerks, saliva may accumulate in the mouth, and the bladder may empty. This is the “clonic” phase. Eventually, the jerking motions diminish and the person regains consciousness, somewhat disoriented and fatigued from the intense muscular activity.

Absence Seizure (formally known as “Petit Mal”)

A generalized seizure, especially prevalent in children three to fourteen years old, is absence. The absence seizure looks considerably milder in form than the tonic-clonic and, in fact, often passes for daydreaming. Thus, the elementary school teacher often notices the disorder before anyone else is aware of it.

A brief lapse of consciousness with staring, eye blinking, or upward rolling of the eyes most commonly characterizes the absence seizure. It is not uncommon for a child to have 50 to 100 absence seizures a day. Most children outgrow this epilepsy at puberty.

Myoclonic Seizure

Myoclonic seizures can be described as jerking or twitching of the body in a muscle or a group of muscles, and are typically brief in duration, usually lasting only a couple of seconds. While people without epilepsy can experience myoclonus, in epilepsy myoclonic seizures usually cause abnormal movements on both sides of the body simultaneously.

• Juvenile myoclonic epilepsy: These seizures usually begin around the time of puberty, and often occur shortly after waking up.
• Progressive myoclonic epilepsy: This form of epilepsy is characterized by a combination of myoclonic and tonic-clonic seizures. These symptoms typically worsen over time and are difficult to control.

Tonic Seizure

Tonic seizures are characterized by the sudden contraction and stiffening of the muscles. Often a person’s eyes may roll back into their head, and as the chest muscles tighten and contract, it may become more difficult to breathe. These seizures are short in duration, and usually last less than 20 seconds.

Clonic Seizure

With clonic seizures, an individual’s muscles begin jerking and spasming repeatedly, and it is important to note that restraining or repositioning the individual cannot stop these seizure movements. Clonic seizures are considered to be rare.

Atonic Seizure

During an atonic seizure, muscles suddenly lose tone (or “strength”) due to temporary changes in brain function. These seizures are brief, and usually last 15 seconds or less. Atonic seizures usually begin in childhood and last into adulthood. Although the individual usually remains conscious and the seizures themselves do not cause any bodily harm, indirect injuries can often occur from falling due to the lack of muscle control. Atonic seizures are also sometimes referred to as “drop seizures” or “drop attacks”.

 

FOCAL SEIZURES – involving a localized area of the brain

Focal seizures (also known as “partial seizures” or “localized seizures”) are usually described by how they look and feel, such as:

• Without impairment of consciousness or awareness
• Involving subjective sensory or psychic phenomena
• With impairment of consciousness or awareness, or dyscognitive
• Evolving to a bilateral convulsive seizure

The different types of focal seizures are categorized/ described by the major types of symptoms of the seizure. The terms “simple partial” and “complex partial” (explained below) are not used to describe a focal seizure if the individual’s consciousness or awareness are affected.

Simple Partial Seizures

Simple partial seizures only affect a small part of the brain, usually the temporal lobes or hippocampi, and are usually brief in duration, lasting only a couple of minutes. Simple partial seizures often precede a complex partial seizure or a tonic-clonic seizure, and in such cases are often referred to as a “seizure aura”. Auras are often characterized by a brief sensation in the stomach or head, such as a sinking or rising feeling, a buzzing sound, an unpleasant odor, or spots before the eyes. Individuals who can train themselves to recognize the start of seizure activity before it spreads to other parts of the brain can use it as a warning to take protective measures to prevent possible injury during the seizure itself.

Complex Partial Seizures (also known as “Temporal Lobe” or “Psychomotor”)

The most common partial seizure is what is now termed complex-partial and formerly was known as temporal lobe or psychomotor. The complex-partial seizure consists of three brief phases: The person stops ongoing activity and assumes a dazed and staring expression. Then a pattern of repititous, automatic, purposeless behavior begins and typically lasts a few minutes. Such behavior may include lip smacking, picking at clothes, buttoning and unbuttoning clothes or finger pulling. As the person returns to consciousness, a short period of disorientation and confusion occurs.

 

Revised Classifications of Seizures
(Report of the ILAE Commission 2005- 2009)

• Generalized seizures
  • Tonic-clonic (of any kind)
  • Absence
    • Typical
    • Atypical
    • Absence with special features
    • Myoclonic absence
    • Eyelid myoclonia
  • Myoclonic
    • Myoclonic
    • Myoclonic atonic
    • Myocloic tonic
  • Clonic
  • Tonic
  • Atonic
• Focal seizures
• Unknown
  • Epileptic Spasms
  • (Events that are not clearly diagnosed into one of the categories above)