A motor onset seizure involves motor activity (movement) and may be due to either an increase or decrease in contraction in a muscle or group of muscles. Depending on the muscle groups involved and the way they are affected, the movement features of a motor onset seizure may be simple or more complex.
NOTE If the focal seizure is not characterized by this feature at the very outset of the seizure, it is not used to classify the seizure, it is instead used as a seizure descriptor, after the seizure is classified according to its onset feature.
Focal clonic seizure - the movement involves sustained rhythmic jerking, this may involve a distal limb, one limb or one side of the body. The jerking may spread to involve parts of the body according to their representation on the motor cortex (according to the homunculus), this is known as a Jacksonian march.
Focal tonic seizure - increased muscle tone, usually lasting for seconds to minutes.
Focal motor seizure with dystonia - a sustained contraction of both agonist and antagonist muscles producing athetoid or twisting movements, which produces abnormal postures.
Focal myoclonic seizure - a single or short cluster of brief muscle contractions (jerks), each jerk is typically milliseconds in duration.
Focal atonic seizure - sudden loss or diminution of muscle tone without apparent preceding myoclonic or tonic activity, typically lasting >500 milliseconds but < 2 seconds. It may involve the head, trunk, jaw or limb musculature.
Focal motor seizure with paresis/paralysis - the seizure onset is characterized by weakness or complete paralysis of a muscle or group of muscles.
Focal epileptic spasms - sudden flexion, extension or mixed flexion-extension of proximal and truncal muscles, lasting 1-2 seconds, typically occurs in a series.
Focal hyperkinetic seizure - this seizure type involves movements of proximal limb or axial muscles, producing irregular large amplitude movements, such as pedaling, pelvic thrusting, jumping, thrashing and/or rocking movements.
Focal automatism seizure - an automatism is a coordinated, repetitive motor activity, often resembling a voluntary movement, but undertaken without volition. They often occur in seizures with impaired awareness, but can occur in aware states. Focal automatism seizures can be further described using the following descriptors:
Focal motor seizure with dysarthria / anarthria - the onset of the seizure is characterized by difficulty with articulation of speech, due to impaired coordination of muscles involved in speech sound production. Receptive and expressive language functions are intact, however speech is poorly articulated and is less intelligible.
Focal motor seizure with negative myoclonus - a sudden interruption in normal tonic muscle activity lasting 500 milliseconds or less, without evidence of preceding myoclonus. This is seen in the epilepsy syndrome atypical childhood epilepsy with centrotemporal spikes, where an upper limb or the head is affected by localized brief interruption in normal muscle tone. The interruption in muscle tone is briefer than seen in a focal atonic seizure. The patient may correct for the loss of tone with overshoot past the primary position.
Focal motor seizure with version - onset of sustained, forced conjugate ocular, cephalic, and/or truncal rotation or lateral deviation from the midline. The laterality is important to specify as this assists in hemispheric lateralization, for example the seizure might be a focal motor seizure with ocular and cephalic version to the right.
Focal bilateral motor seizure -the seizure commences in one hemisphere but involves bilateral muscle groups rapidly at seizure onset. Certain frontal lobe seizure sub-types have bilateral motor features at onset, often with asymmetric posturing. Typically, there is extension of the upper limb (at the elbow) contralateral to the hemisphere of seizure onset (often with a clenched fist and flexion at the wrist) and flexion of the ipsilateral upper limb at the elbow. This type of seizure is also described as a 'fencer's posture' or a 'figure of 4'. Awareness can be preserved during the bilateral movement, resulting in misdiagnosis of the seizure as a non-epileptic seizure. These seizures can progress to a focal to bilateral tonic-clonic seizure.
Epilepsia partialis continua refers to recurrent focal motor seizures (typically affecting hand and face, although other body parts may be affected), that occur every few seconds or minutes for extended periods (days or years). The focal motor features may exhibit a Jacksonian march. A Todd's paresis may be seen in the affected body part.