What is multiple sclerosis? 

Multiple sclerosis (MS) affects nerves in the brain and spinal cord, causing a wide range of symptoms including problems with muscle movement, balance and vision.

Each nerve fibre in the brain and spinal cord is surrounded by a layer of protein called myelin, which protects the nerve and helps electrical signals from the brain travel to the rest of the body. In MS, the myelin becomes damaged.

This disrupts the transfer of these nerve signals, causing a wide range of potential symptoms, such as loss of vision, uncontrolled muscle movements, difficulties with balance and co-ordination, and fatigue. 

MS is an autoimmune condition. This means your immune system mistakes the myelin for a foreign substance and attacks it. The myelin becomes inflamed in patches (called plaques or lesions), which can be seen on an MRI scan.

This can disrupt the messages travelling along nerve fibres. It can slow them down, or even stop them from getting through completely.

When the inflammation goes away, it can leave behind scarring of the myelin sheath (known as sclerosis). These attacks can damage the myelin sheath, a process called demyelination.

In addition to the myelin sheath covering being damaged, MS can also damage the underlying nerve fibre called axons. It is thought that axonal damage is the main cause of disability and disease progression in MS. 

Who is affected?

It is estimated that there are currently around 100,000 people with MS in the UK.

MS is most commonly diagnosed in people aged 20 to 40, although it can happen at any age.

For reasons that are unclear, MS is three times more common in women than men.

MS can be a challenging and frustrating condition to live with but new treatments over the past 20 years have considerably improved the quality of life of people with the condition.

MS is not fatal, but some complications that can arise from severe MS, such as pneumonia, can be.

As a result, the average life expectancy for people with MS is around five to 10 years lower than the population at large. This gap appears to be getting smaller, perhaps because of improved medical care.

Causes of MS

The exact reason why someone develops MS is not known. What is known so far suggests it is caused by a combination of environmental and genetic factors.

Why do people develop MS?

It is not understood what causes the immune system to attack myelin, although there are several theories. Most experts agree that MS is probably caused by a combination of genetic and environmental factors. This means it's partly caused by gene pool and partly caused by outside factors that may trigger the condition.

Genetic factors

MS is not defined as a genetic condition because there is no single gene that causes it. It's not directly inherited, although research has shown people who are related to someone with MS are more likely to develop it.

Researchers have found that if one twin develops MS then the second twin has around a one in four chance of also developing MS.

The chance of a brother, sister or child of a person with MS also developing MS themselves is less than one in 30.

It's possible that different combinations of genes make developing MS more likely, and research into this is continuing. However, genetic theories cannot explain the wide variation in occurrences of MS throughout the world.

Sunlight and vitamin D

Research into MS around the world has shown that it's more likely to occur in countries far from the equator. For example, MS is relatively common in the UK, North America and Scandinavia, where the winter season is longer than in the Southern hemisphere.

It’s possible that people living further from the equator are exposed to less sunlight and, therefore, have less vitamin D in their bodies. Some studies have found a link between lower levels of vitamin D and incidence of MS.

Some researchers have suggested that vitamin D supplements may reduce the risk of MS. However, this has not been proven.

Smoking

Smoking is another factor that appears to increase someone’s risk of developing progressive MS. It is not yet clear exactly why this is, although one theory is that the chemicals in the cigarette smoke affect the immune system.

Viral infection

Another theory is that common viruses may be involved in the development of MS. The Epstein-Barr virus (EBV) and herpes, which is a very common virus that causes glandular fever, has been the subject of most of the current studies.
More research is needed to further understand how EBV may increase the risk of developing MS.

MS symptoms

There are many different symptoms of MS and they affect each person differently. Most people with MS only have a few symptoms and it is unlikely someone would develop all possible symptoms.

The central nervous system (brain and spinal cord) controls all of your body's actions. When MS damages the myelin coating around the nerve fibres that carry messages to and from your brain, symptoms can occur in any part of your body.

The symptoms are unpredictable. Some people's MS symptoms develop and increase steadily over time, while for others, they come and go periodically.

These periods when symptoms get worse are known as relapses. Periods when symptoms improve or disappear are known as remissions.

  • Visual problems

    In around one in five cases of MS, the first noticeable symptom is problems with one of your eyes. You may experience:
    • some loss of vision in the affected eye – this can range from mild to severe (total loss of vision occurs in one in 35 cases)
    • colour blindness 
    • eye pain; usually made worse when moving the eye
    • flashes of light when moving the eye

    These symptoms are the result of optic neuritis, which is inflammation (swelling) of the optic nerve that transmits visual information to the brain. This normally only affects one eye.

    Other visual problems that can occur in MS include:

    • double vision 
    • eye pain in both eyes
    • involuntary eye movements (usually from side to side), known as nystagmus
  • Bladder problems

    Bladder problems are common in MS. They may include:
    • difficulty emptying the bladder completely
    • having to urinate more frequently
    • having a sudden, urgent need to urinate which can lead to unintentionally passing urine (urge incontinence)
    • having to get up frequently during the night to pass urine (nocturia)
  • Bowel problems

    Many people with MS have problems with their bowel.
     
    Constipation is the most common problem, affecting around half of people with MS. They may pass stools much less frequently than normal, and find this difficult.

    Bowel incontinence is less common but is often linked to constipation. If a stool becomes stuck, it can irritate the wall of the bowel, causing it to produce more fluid and mucus that can leak out of the anus (back passage).
  • Speech and swallowing difficulties

    Around a third of people with MS experience difficulty chewing or swallowing (dysphagia) at some point. In some cases, speech may also become slurred, or difficult to understand.

    However, for most people with MS, speech and swallowing symptoms are mild and only last for a few minutes at a time. They are often at their worst during a relapse.
  • Abnormal sensations

    Abnormal sensations can also be a common initial symptom of MS. This can take the form of numbness or tingling in different parts of your body.
     
    Muscles in your arms and legs may also feel unusually weak.
  • Muscle spasms and spasticity

    If messages between your brain and muscles are disrupted, this can cause problems with muscle movements. It can cause muscles to contract tightly and painfully (spasm) or your muscles may also become stiff and resistant to movement, known as spasticity.
  • Pain

    Around half of people with MS experience pain, which can take two forms:
    • Neuropathic pain – caused by damage to the nerve fibres in the brain and spinal cord. It can be a stabbing pain, extreme skin sensitivity, or a burning sensation.
    • Musculoskeletal pain – this is not caused directly by MS, but can occur if there is excess pressure on muscles or joints as a result of spasms and spasticity.
  • Mobility problems

    MS can affect balance and co-ordination. It can make walking and moving around difficult, particularly if you also have muscle weakness and spasticity. You may experience:
    • ataxia – difficulty with co-ordination
    • tremor – shaking of the limbs, which is rare, but can be severe
    • dizziness and vertigo can happen late on and can make you feel as if your surroundings are spinning
  • Extreme tiredness (fatigue)

    Feeling extremely tired (fatigue) is a common symptom of MS that many people describe as one of the most troublesome.

    It is estimated that as many as nine out of 10 people with MS will experience episodes of fatigue.

    People with MS have reported feeling an overwhelming sense of weariness where even the most simple physical or mental activity seems to be a tremendous struggle to carry out.
    Fatigue may be worse in hot weather, after exercising, or during illness.
  • Problems with thinking, learning and planning

    Around half of people with MS have problems with thinking, learning and planning (known as cognitive dysfunction). They may experience:
    • problems understanding and using language
    • a shortened attention span
    • problems learning and remembering new things (long-term memory is usually unaffected)
    • problems understanding and processing visual information, such as reading a map
    • difficulty with planning and problem solving – people often report that they know what they want to do, but can’t grasp the method of how to do it
    • problems with reasoning, such as mathematical laws or solving puzzles
  • Mental health issues

    Around half of all people with MS experience at least one episode of depression at some point in their life.
     
    It is unclear whether the depression arises from the damage to the brain caused by MS, or due to the stress of having to live with a long-term condition, or both.

    Anxiety can also be a problem for people with MS, possibly due to the unpredictable nature of the condition.

    Some people with MS can sometimes experience rapid and severe mood swings, suddenly bursting into tears, laughing or shouting angrily for no apparent reason.
  • Sexual problems

    MS can have an effect on sexual function.

    Men with MS often find it hard to obtain or maintain an erection (erectile dysfunction). They may also find it takes a lot longer to ejaculate when having sex or masturbating, and may even lose the ability to ejaculate altogether.

    For women, problems include difficulty reaching orgasm as well as decreased vaginal lubrication and sensation.

    Both men and women with MS may find they are less interested in sex than they were before. This could be directly related to the MS, or it could be the result of living with the condition.