Causes of cerebral palsy

Cerebral palsy is caused by a problem in the parts of the brain responsible for controlling movement. It can occur if the brain is damaged in early lifeor develops abnormally, although the exact cause isn't always obvious.

Parts of the brain responsible for other important functionsmay also be affected, such as:

• communication
• hearing
• vision
• the ability to learn

This is why people withcerebral palsycan have various other problems which don'tinvolve the muscles.

What causes the problems in the brain?

In the past, doctors believed cerebral palsy was usually caused by brain damage sustained during birth the direct result of being temporarily deprived of oxygen (asphyxiation). Asphyxiation can sometimes occur during a difficult or complicated birth.

However, a major research project carried out in the 1980s showed that in babies born at term,asphyxiation was responsible forless than 10% of cerebral palsy cases. Most were due to problems with the brain that developed before the child was born.

Researchers believe there are three main problems that can affect the brain before birth and cause cerebral palsy:

• periventricularleukomalacia (PVL)damage of the brain's white matter
• abnormal development of the brain
• intracranial haemorrhage and stroke

These are discussed below.

Periventricular leukomalacia (PVL)

PVL is also known as white matter damage (WMD) of prematurity.

The white matterpart of the brain is made up of many nerve fibres, which are protected by a white fatty protein, known as myelin. White matter is responsible for directing communication between the movement and thought-processing sections of the brain (known as grey matter) and the rest of the body.

It's thought that the brain damage is caused by a reduction in the childs blood or oxygen supply, which damages the brain cells. This has serious consequences in later life, as the white matter is responsible for transmitting signals from the brain to the muscles.

It's not clear exactly why PVL occurs, but it's been linked to:

• an infection caught by the mother
• the mother having abnormally low blood pressure
• premature birth , especially if a child is born at 32 weeks of pregnancy or earlier

Abnormal development of the brain

Anything that changes or affects the brain's normal structural development can lead to problems with the way it transmits information to the muscles. If this happens, a child can develop cerebral palsy.

Brain development can be affected by:

• changes (mutations) in the genes thatplay a role in the brain's development
• an infection caught by the mother
• trauma or injury to the unborn baby's head

Stroke

Most strokes are caused by a blockage cutting off the blood supply to the brain (ischaemic stroke). However, strokes can also be caused by bleeding in or around the brain (haemorrhagic stroke). The result of both of these events is that brain tissue is damaged.Thisis the most common cause of hemiplegic cerebral palsy.

Intracranial haemorrhage is normally seen in babies born prematurely, although it sometimes occurs in unborn babies after they've had a stroke .

Factors that increase the risk of an unborn baby having a stroke include:

• pre-existing weaknesses or abnormalities in the baby's blood vesselsor the mothers placenta
• high blood pressure in the mother
• the mother having an infection during pregnancyparticularly pelvic inflammatory disease
• twin pregnancy where there is early loss of one twin during the pregnancy

Brain damage during or after birth

Afew cases of cerebral palsy are caused by brain damage that occurs during or soon after birth.

Damage can be caused by:

• asphyxiation when the child is born
• an infection of the brain such as meningitis
• a particularly low blood sugar level (hypoglycaemia)
• a serious head injury
• a stroke