Cerebral palsy is the result of damage to the brain so is primarily classed as a neurological condition. However, its most obvious effects on the body are an impairment of movement, posture and coordination, so it is also considered an orthopaedic and neuromuscular condition.
The brain is either damaged or develops abnormally, often before birth, and cerebral palsy mostly afflicts children under three years old. The brain damage or abnormalities do not progress with age, meaning that cerebral palsy is a ‘static’ condition where the brain damage does not get any worse (nor does it improve). However, some of its effects on the body may become slightly more or less pronounced over time.
It is not a single condition - there is no clear and singular cause - so no two cases of cerebral palsy are exactly the same, making it difficult to study and categorise. On the one hand, it can affect some people mildly, but for others it can be very severe and debilitating.
There can also be some incapacitating secondary complications from cerebral palsy such as epilepsy, learning difficulties, ADHD and loss of hearing amongst others.
Of the three main categories, spastic cerebral palsy is the most common, affecting just under 80% of all people with the condition.
It is the result of an abnormality in the brain called an upper motor neuron lesion, which prevents the brain from sending some necessary electrical signals to the muscles. In severe cases, its effects are noticeable enough to be diagnosed within the first year of life. However, children with milder symptoms may go undiagnosed until reaching three years of age.
Spastic cerebral palsy is characterised by stiff and jerky movements in affected areas, and the parts of the body that this involves classifies the condition further:
Hemiplegia – this is when one side of the body is affected, the leg and arm in particular
Diplegia – this is when the lower half of the body is predominantly affected. The arms are either not affected, or are slightly affected at most
Quadriplegia – in this case both the arms and the legs are affected, the arms usually more so than the legs
Less commonly, there are also the following two (very rare) types:
Monoplegia – where one limb is affected
Triplegia – where three limbs are affected
Using this categorisation method, two examples would be spastic diplegic cerebral palsy or spastic quadriplegic cerebral palsy.
Much less common than spastic cerebral palsy, athetoid cerebral palsy is estimated to affect between 10 to 20% of all people with the condition and is usually diagnosed within 18 months of birth.
Athetoid cerebral palsy, also sometimes known as dyskinetic cerebral palsy, occurs through damage to the basal ganglia, a part of the brain that controls coordination and movement. This results in an alternation between both excessive muscle tone (a stiffness of the muscles known as hypertonia) and low muscle tone (a weakness in the muscles called hypotonia), which causes involuntary slow and writhing movements in the limbs and trunk of the body.
Athetoid dyskenetic cerebral palsy has two further sub-category groups: choreoathetoid cerebral palsy (where involuntary movement and spasms primarily affect the extremities and the face) and dystonic cerebral palsy (where dystonia occurs i.e. slow and writhing contractions that are more pronounced either in isolated regions or alternatively, across the whole of the body).
Generally, as severe cases tend to affect several areas of the body, including all limbs, the face and the trunk, athetoid cerebral palsy can often be classified as athetoid quadriplegic cerebral palsy.
Ataxic cerebral palsy is the least common of the main categories and is relatively rare, affecting less than 10% of all known cases.
It is usually developed either prior to or during birth and is the result of complications during pregnancy causing damage to the cerebellum, a region at the base of the brain vital for motor control. However, ataxic cerebral palsy can also occur after illnesses such as meningitis or a severe head trauma.
Ataxic cerebral palsy causes tremors and difficulties in walking, of which will be discussed further in the effects of cerebral palsy section.
Although there are three main categorisations of cerebral palsy, it is not uncommon for there to be a combination of two or more of the categories present at the same time. These cases are called mixed cerebral palsy.
For example, the most common mixed form is the muscle-tightening spastic cerebral palsy combined with the involuntary movements of athetoid cerebral palsy. This is the result of injuries to two parts of the brain known as the pyramidal and extrapyramidal areas.
Although spastic athetoid cerebral palsy is the most common of the mixed category, various combinations are possible, with athetoid and ataxic mixed cerebral palsy the least common.
Find out more about CP's many possible symptoms in our detailed effects of cerebral palsy section.