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Somewhere between 11% and 20% of children born with cerebral palsy will have primarily athetoid (or dyskinetic) symptoms. That makes this disorder the second most common form of cerebral palsy (CP), a group of neuromuscular conditions that affect the way a person moves.
What Is Athetoid Cerebral Palsy?
Caused by brain damage or abnormal development, athetoid forms of CP often cause involuntary movements, which can be fast or slow, but usually make walking, sitting and maintaining balance difficult for children.
Hypertonia & Hypotonia
Some children with athetoid-forms of cerebral palsy will present symptoms related to both hypertonia and hypotonia, two abnormal states of muscle tone.
At rest, our muscles maintain a base level of tension, according to the University of California Los Angeles’ Center for Cerebral Palsy. Muscles are partially contracted at all times, maintaining posture and balance, while allowing quick snaps of action when reflexes become necessary. Cerebral palsy disorders, in general, are characterized by abnormalities in muscle tone – the resting state of a muscle.
- Hypertonia – excessive muscle tone – often used as a synonym for the more-specific concept of “spasticity,” hypertonia is characterized by hyperactive motor neurons. These neurons fire on a hair-trigger, often due to brain damage that mixes up the way neural signals are transmitted from the brain through the spinal cord. Hypertonia causes a myriad of potential symptoms, from muscle spasms to rigidity. Children with hypertonic disorders often struggle to move their affected limbs freely, appearing stiff or “out of control.”
- Hypotonia – deficient muscle tone – the flip-side of hypertonia, hypotonia involves muscles that are always too lose, lacking the baseline tension that allows people without hypotonic disorders to maintain their posture and balance at rest. As a result, children with hypotonia often have extremely mobile joints and poor reflexes.
People with athetoid cerebral palsy can oscillate between these two states, displaying symptoms of both hypertonia and hypotonia. Their brains, usually because of damage to the basal ganglia, have lost the ability to control muscle tone.
In most medical circles, the term “athetoid” cerebral palsy is more closely-associated with low muscle tone, which makes children and adults unstable in their postures and voluntary movements. When high muscle tone is also involved, the disorder is known technically as athetoid dyskinetic cerebral palsy and usually results in muscle spasms, which can cause patients pain.
These names haven’t really been standardized. Sometimes, you’ll see dyskinetic (or dystonic) cerebral palsy and athetoid cerebral palsy used as synonyms for each other. In other places, you might see dyskinetic CP used to describe a broad category of neuromuscular disorders, only one of which is athetoid cerebral palsy.
Brain Damage & The Basal Ganglia
Cerebral palsy is caused by brain damage. Researchers have identified three basic ways this sort of brain damage can occur:
- Genetic abnormalities – some children’s brains don’t develop properly before birth, due to genetic mutations, which can either be random side effects of fetal development or (many researchers think) inherited from a parent
- Birth injuries – other children will suffer brain damage during or soon after childbirth, due either to oxygen deprivation during labor or delivery or severe cases of jaundice
- Maternal complications – some maternal infections can pass through the placental barrier and harm the way a developing child grows. Alternatively, preexisting medical conditions (like high blood pressure) can affect the way oxygen is delivered to the child. In either case, infant brain damage may be a tragic result.
No matter the exact cause, physicians believe that the vast majority of cerebral palsy cases that involve athetoid or dyskinetic symptoms involve damage to the basal ganglia, a group of bundled neurons at the bottom of the forebrain.
Recent progress in neuroscience has shown that neurons in the basal ganglia do a lot, playing roles in complex processes like emotion and motivation. The basal ganglia’s central role, however, likely lies in the domain of movement, notably the control of voluntary movements – ones we intend to make. Signals from the cerebrum and the spinal cord flow through the basal ganglia, transmitting information on when and how to activate or inhibit the body’s motor neurons. Damage that part of the brain and motor control is disrupted, too.
Two Aspects Of Movement
A recent article at Boundless.com explains how scientists first discovered the basal ganglia’s importance in movement by studying two neurological disorders: Parkinson’s disease and Huntington’s disease. In many ways, these two disorders mirror the effects of athetoid and dyskinetic symptoms in people with cerebral palsy.
Parkinson’s causes a prolonged decrease in a person’s ability to initiate movements, similar to the ineffective and loose muscles that characterize athetoid forms of CP. Huntington’s, on the other hand, is almost the exact opposite, as patients become unable to stop involuntary movements from occurring. That sounds a lot like the muscle spasms that mark cases of dyskinetic cerebral palsy.
In short, muscles can too much, too little or both, all because the basal ganglia have stopped working properly.
Symptoms & Signs
The primary symptom associated with athetoid and dyskinetic cerebral palsy disorders is involuntary movement, small or large movements that occur without being intended. In basic terms, these movements can be split into two categories:
- athetosis – slow, continuous writhing movements (usually in the hands and feet)
- dystonia – repetitive twisting movements, caused by prolonged muscle contractions
- chorea – small, quick movements that are unpredictable, not repetitive (many researchers consider chorea to be “semi-purposeful,” because milder spasms can be incorporated into voluntary movements)
These movement disorders aren’t isolated from one another. Instead, they exist on a spectrum, running from mild to violent, staccato to smooth and brief to prolonged. Severe cases of chorea, for example, can result in such violent flailing movements that doctors consider it a separate medical disorder, ballismus. Likewise, the slow writhing motions characteristic of athetosis can become so quick that they turn into a variant of chorea, in a condition termed choreoathetosis.
Complications & Diagnosis
Paired with their oscillations in muscle tone, these involuntary movements make it hard for cerebral palsy patients to hold their posture and maintain balance. Sitting, standing and walking can all be difficult, as can movements that require coordination between multiple body parts. Involuntary movements caused by natal brain damage can persist during sleep and become more extreme during periods of emotional intensity.
Most cases of the disorder are diagnosed before the age of three, but apparently involuntary movements, a cause for concern, can certainly be observed long before that. Developmental motor delays are often first noticed by parents:
- inability to sit upright
- inability to hold head up by three months
- inability to reach for objects
- difficulty crawling or walking
Doctors usually use the Gross Motor Function Classification System, a clinical test that evaluates the patient’s ability to sit, walk or wheel, to confirm diagnosis and grade the condition’s severity. MRI scans of the brain have also shown promise in diagnosing athetoid cerebral palsy early, but remain far from perfect.
While most children will have the disorder’s primary effects in their limbs and trunk, dyskinetic cerebral palsy can also impact the muscles of the face and tongue, leading to involuntary facial movements and drooling. This can also make it hard for people with cerebral palsy to eat. Cases of CP that affect the mouth often result in speech and language disorders, particularly common for patients with dyskinetic or athetoid symptoms. Technically, speech disorders caused by neuromotor problems are referred to as “dysarthria,” with a difficulty articulating speech sounds being the most frequent issue.
Treating Athetoid Cerebral Palsy
Cerebral palsy is a nonprogressive, but permanent, disorder. In other words, the underlying brain damage that causes a child’s neuromuscular problems doesn’t get worse over time, but it doesn’t get better, either. The manifestations of cerebral palsy, on the other hand, can change drastically as a child ages, which means the best treatment methods will likely change, too.
There is no cure for CP, but a variety of therapies and medications can help children with the disorder capitalize on their existing abilities and create new solutions to their challenges.
Physical & Occupational Therapy
Occupational and physical therapy are usually the first-line of treatment. Experienced physical therapists can help children with cerebral palsy develop muscle strength and tone through specialized exercises. Occupational therapists, on the other hand, help kids tackle everyday tasks that might be hard for them.
These specialists work on functional issues and fine motor skills, aiding children in developing the ability to play and learn effectively. Occupational therapists can also help train kids with cerebral palsy to use assistive devices, like walkers and communication supports.
The primary class of drugs used to treat people with athetoid CP are called anticholinergic medications, which block the action of a neurotransmitter, acetylcholine, that can trigger motor nerve impulses. As a result, anticholinergic drugs can reduce the severity or frequency of involuntary muscle movements. The medications are often used to reduce drooling.
Drugs can also be helpful in treating associated conditions that occur frequently in people with cerebral palsy, like seizures.
Surgery is rare for children with athetoid forms of cerebral palsy. Most surgical treatments are reserved for patients who experience primarily hypertonic side effects, ones caused by high muscle tone. In these cases, surgeons can replace over-tightened tendons, sever muscles that trigger too much or correct maldevelopment of body structures that can occur as a secondary result of their cerebral palsy.