Classification Based on Motor Function

The major categories are:

Spastic
Athetoid
Hypotonic
Ataxic
Mixed
Spastic Quadriplegia
Spastic Diplegia

The brain injury that causes cerebral palsy affects motor function, the ability to control the body in a desired matter. Two main groupings include spastic and non-spastic. Each has multiple variations and it is possible to have a mixture of both types.

Spastic cerebral palsy is characterized by increased muscle tone.
Non-spastic cerebral palsy will exhibit decreased or fluctuating muscle tone.

Motor function classification provides both a description of how a child’s body is affected and the area of the brain injury. Using motor function gives parents, doctors, and therapists a very specific, yet broad, description of a child’s symptoms, which helps doctors choose treatments with the best chance for success.

Muscle Tone

Many motor function terms describe cerebral palsy’s effect on muscle tone and how muscles work together. Proper muscle tone when bending an arm requires the bicep to contract and the triceps to relax. When muscle tone is impaired, muscles do not work together and can even work in opposition to one another.

Two terms used to describe muscle tone are:

Hypertonia/Hypertonic — increased muscle tone, often resulting in very stiff limbs. Hypertonia is associated with spastic cerebral palsy

Hypotonia/Hypotonic — decreased muscle tone, often resulting in loose, floppy limbs. Hypotonia is associated with non-spastic cerebral palsy

Two Classifications by Motor Function: Pyramidal and Extrapyramidal

When referring to location of the brain injury, spastic and non-spastic cerebral palsy is referred to in the medical community as pyramidal (spastic) and extrapyramidal (non-spastic) cerebral palsy.

The pyramidal tract consists of two groups of nerve fibers responsible for voluntary movements. They descend from the cortex into the brain stem. In essence, they are responsible for communicating the brain’s movement intent to the nerves in the spinal cord that will stimulate the event. Pyramidal cerebral palsy would indicate that the pyramidal tract is damaged or not functioning properly.

Extrapyramidal cerebral palsy indicates the injury is outside the tract in areas such as the basal ganglia, thalamus, and cerebellum. Pyramidal and extrapyramidal are key components to movement impairments.

Spastic (Pyramidal) – Spasticity implies increased muscle tone. Muscles continually contract, making limbs stiff, rigid, and resistant to flexing or relaxing. Reflexes can be exaggerated, while movements tend to be jerky and awkward. Often, the arms and legs are affected. The tongue, mouth, and pharynx can be affected, as well, impairing speech, eating, breathing, and swallowing.

Spastic cerebral palsy is hypertonic and accounts for 70% to 80% of cerebral palsy cases. The injury to the brain occurs in the pyramidal tract and is referred to as upper motor neuron damage.

The stress on the body created by spasticity can result in associated conditions such as hip dislocation, scoliosis, and limb deformities. One particular concern is contracture, the constant contracting of muscles that results in painful joint deformities.

Spastic cerebral palsy is often named in combination with a topographical method that describes which limbs are affected, such as spastic diplegia, spastic hemiparesis, and spastic quadriplegia.

Non-Spastic (Extrapyramidal) – Non-spastic cerebral palsy is decreased and/or fluctuating muscle tone. Multiple forms of non-spastic cerebral palsy are each characterized by particular impairments; one of the main characteristics of non-spastic cerebral palsy is involuntary movement. Movement can be slow or fast, often repetitive, and sometimes rhythmic. Planned movements can exaggerate the effect – a condition known as intention tremors. Stress can also worsen the involuntary movements, whereas sleeping often eliminates them.

An injury in the brain outside the pyramidal tract causes non-spastic cerebral palsy. Due to the location of the injury, mental impairment and seizures are less likely. Non-spastic cerebral palsy lowers the likelihood of joint and limb deformities. The ability to speak may be impaired as a result of physical, not intellectual, impairment.

Non-spastic cerebral palsy is divided into two groups, ataxic and dyskinetic. Together they make up 20% of cerebral palsy cases. Broken down, dyskinetic makes up 15% of all cerebral palsy cases, and ataxic comprises 5%.

Ataxic/Ataxia

Ataxic cerebral palsy affects coordinated movements. Balance and posture are involved. Walking gait is often very wide and sometimes irregular. Control of eye movements and depth perception can be impaired. Often, fine motor skills requiring coordination of the eyes and hands, such as writing, are difficult.

Dyskinetic

Dyskinetic cerebral palsy is separated further into two different groups; athetoid and dystonic.

Athetoid cerebral palsy includes cases with involuntary movement, especially in the arms, legs, and hands.

Dystonia/Dystonic cerebral palsy encompasses cases that affect the trunk muscles more than the limbs and results in fixed, twisted posture.

Because non-spastic cerebral palsy is predominantly associated with involuntary movements, some may classify cerebral palsy by the specific movement dysfunction, such as:

Athetosis — slow, writhing movements that are often repetitive, sinuous, and rhythmic

Chorea — irregular movements that are not repetitive or rhythmic, and tend to be more jerky and shaky

Choreoathetoid — a combination of chorea and athetosis; movements are irregular, but twisting and curving

Dystonia — involuntary movements accompanied by an abnormal, sustained posture

Ataxia/Ataxic — does not produce involuntary movements, but instead indicates impaired balance and coordination

Mixed

A child’s impairments can fall into both categories, spastic and non-spastic, referred to as mixed cerebral palsy. The most common form of mixed cerebral palsy involves some limbs affected by spasticity and others by athetosis.

Information adapted from http://cerebralpalsy.org/about-cerebral-palsy/types/ and other sources.

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