The four most common causes of paralysis are stroke, head injury, spinal cord injury and multiple sclerosis.
A stroke is a serious medical condition that occurs when the blood supply to your brain is disturbed.
Like all organs, the brain needs a constant supply of blood that contains oxygen and nutrients to function properly.
If the blood supply is restricted or stopped, brain cells will begin to die, which can lead to brain damage that often results in paralysis.
Read more about stroke.
A severe head injury can cause brain damage. The brain's surface can tear or bruise as it bumps against the skull, damaging blood vessels and nerves.
Paralysis can occur if a part of the brain that controls specific muscles is damaged during a severe head injury.
Damage to the left side of the brain can cause paralysis on the right side of the body, and damage to the right side of the brain can cause paralysis on the left side of the body.
Read more about severe head injury.
Spinal cord injury
The spinal cord is part of your central nervous system. It is a thick bundle of nerves that runs from your brain, down through the neck and spine, inside a canal of vertebrae.
Its main function is to transmit signals to and from the brain and body. For example, the spinal cord passes nerve signals, such as hot or cold sensations, back to the brain.
If the neck or spine is injured, the spinal cord can also be damaged. This means the brain may no longer be able to transmit signals to the muscles, causing paralysis.
The exact location where the spinal injury occurs can have a significant effect on how severe and wide-ranging the paralysis is. The higher up the spine the injury occurs, the worse the paralysis will be. For example, an injury in the middle of the spine will usually cause paraplegia (paralysis of the lower limbs).
A neck injury, such as a broken neck, will usually result in tetraplegia (paralysis in all four limbs, also known as quadriplegia), as well as loss of normal lung function, which means the person will need to use a ventilator to breathe.
Read more about how the level of spinal cord injury is determined.
The most common causes of spinal cord injury are:
- motor vehicle accidents
- accidents while working
- accidents during sports or other types of activity
- spinal cord paralysis caused by disease rather than injury
The nature of these causes means that most spinal cord injuries occur in men (who account for 80% of all cases) and younger people. It is estimated that half of all spinal cord injuries occur in people who are 16 to 30 years of age.
Multiple sclerosis (MS) is a condition where nerve fibres in the spinal cord become damaged by the immune system (the body's natural defence against infection and illness).
The immune system mistakenly attacks a substance called myelin, which surrounds nerve fibres and helps with the transmission of nerve signals.
In MS, the myelin around the nerve fibres becomes damaged, which disturbs the messages coming to and from the brain. This can result in paralysis.
Read more about multiple sclerosis.
Less common causes of paralysis
There are also a number of less common causes, which are listed below.
Cancers that develop in the brain, such as a high-grade brain tumour, can cause paralysis, usually on one side of the body.
Alternatively, cancers can spread (metastasise) from other parts of the body into the brain or spinal cord, leading to paralysis.
Cerebral palsy is a set of neurological conditions (those that affect the brain and nervous system) that affect a child's movement and co-ordination.
Cerebral palsy is caused by brain damage, which usually occurs before, during or soon after birth. Some possible causes of cerebral palsy include:
- infection during early pregnancy
- a difficult or premature birth
- bleeding in the baby's brain
- abnormal brain development in the baby
The most severe type of cerebral palsy is called spastic quadriplegia, where a person has such a high degree of muscle stiffness (spasticity) in all of their limbs that they are unable to use them.
Read more about cerebral palsy.
Friedreich's ataxia is a rare genetic condition that affects around 1 in every 25,000 people in England. It is caused by a mutation in a gene known as the GAA gene.
The mutation results in the body not producing enough of the protein frataxin. Frataxin is thought to play a role in the regulation of iron levels inside nerve cells.
Because of the lack of enough frataxin being produced, the level of iron and other toxic substances starts to build up inside the nerve cells, damaging them.
Many people with Friedreich's ataxia experience a gradual increase of paralysis in their legs. They will eventually need to use a wheelchair or another type of mobility aid.
Guillain-Barré syndrome is a rare and poorly understood condition caused by peripheral nervous system damage. The peripheral nervous system is the network of nerves that controls the body's senses and movements.
In Guillain-Barré syndrome, the body's immune system attacks the nerves of the peripheral nervous system, which causes them to become inflamed.
This nerve damage results in a tingly, numb sensation in the arms and legs, which can eventually lead to temporary paralysis of the arms, legs and face.
Most people with Guillain-Barré syndrome make a full recovery in a few weeks or months and do not experience any other associated problems.
Read more about Guillain-Barré syndrome.
Lyme disease is a bacterial infection spread by infected ticks.
Ticks are small arachnids that feed on the blood of mammals, including humans. The ticks release bacteria that can damage the nerves, leading to temporary paralysis of the face.
Read more about Lyme disease.
Motor neurone disease
Motor neurone disease (MND) is a rare, incurable condition. Over time, the nerves in the brain and spine gradually lose function (neurodegeneration).
Nerve cells known as motor neurones are affected by MND. Motor neurones are specialised nerve cells that control voluntary muscle movements, such as walking. MND causes progressive muscle weakness, which eventually leads to total body paralysis.
Read more about motor neurone disease.
Spina bifida is a term that describes a series of birth defects that affect development of the spine and nervous system.
Myelomeningocele is the most serious type of spina bifida, occurring in 1 in every 1,000 births. It causes extensive damage to the nervous system, which can often result in partial or total permanent paralysis of the lower limbs.
Read more about spina bifida.