How are seizures classified?

One of the first priorities facing the physician when evaluating a patient with epileptic seizures is to determine seizure type and, when possible, epileptic syndrome. This determination is critical because seizure type and epileptic syndrome to a great extent determine the type of evaluation the patient will receive, as well as the type of therapy.

Seizures are classified into two basic groups, partial and generalized (see list below).

Partial seizures involve only a portion of the brain at the onset. They can be further divided into two types:

• simple partial, in which consciousness is not impaired
• complex partial, in which consciousness is impaired

Both types of partial seizures can spread, resulting in secondarily generalized tonic-clonic seizures.

Generalized seizures are those in which the first clinical changes indicate that both hemispheres are initially involved. Consciousness usually is impaired during generalized seizures, although some seizures, such as the myoclonic type, may be so brief that impairment of consciousness cannot be assessed.

International Classification of Epileptic Seizures1

I. Partial seizures

A. Simple partial seizures

1. With motor signs

a. Focal motor without march

b. Focal motor with march (Jacksonian)

c. Versive

d. Postural

e. Phonatory

2. With somatosensory or special-sensory symptoms

a. Somatosensory

b. Visual

c. Auditory

d. Olfactory

e. Gustatory

f. Vertiginous

3. With autonomic symptoms or signs

4. With psychic symptoms

a. Dysphasia

b. Dysmnesic

c. Cognitive

d. Affective

e. Illusions

f. Structured hallucinations

B. Complex partial seizures

1. Simple partial seizures at onset, followed by impairment of consciousness

a. With simple partial features

b. With automatisms

2. With impairment of consciousness at onset

a. With impairment of consciousness only

b. With automatisms

C. Partial seizures evolving to secondarily generalized seizures

1. Simple partial seizures evolving to generalized seizures

2. Complex partial seizures evolving to generalized seizures

3. Simple partial seizures evolving to complex partial seizures evolving to generalized seizures

II. Generalized seizures

A. Absence seizures

1. Typical absence seizures

a. Impairment of consciousness only

b. With mild clonic components

c. With atonic components

d. With tonic components

e. With automatisms

f. With autonomic components

2. Atypical absence seizures

B. Myoclonic seizures

C. Clonic seizures

D. Tonic seizures

E. Tonic-clonic seizures

F. Atonic seizures

Adapted from: Holmes GL. Classification of seizures and the epilepsies. In: Schachter SC, Schomer DL, eds. The comprehensive evaluation and treatment of epilepsy. San Diego, CA: Academic Press; 1997. p. 1-36.
With permission from Elsevier (www.elsevier.com)
Reviewed and revised January 2004 by Gregory L. Holmes, MD, Dartmouth Medical School