What is multiple sclerosis?

NHS choices definition for multiple sclerosis

Multiple sclerosis (MS) is a disease affecting nerves in the brain and spinal cord, causing 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 – usually only in one eye
  • spasticity – muscle stiffness that can lead to uncontrolled muscle movements
  • ataxia – difficulties with balance and coordination
  • fatigue – feeling very tired during the day

Types of multiple sclerosis

Around 8 out of 10 people with MS will have the relapsing-remitting type of MS.

Someone with relapsing-remitting MS will have periods of time where symptoms are mild or disappear altogether. This is known as remission and can last for days, weeks or sometimes months.

Remission will be followed by a sudden flare-up of symptoms, known as a relapse. Relapses can last from a few weeks to few months.

Usually after around 10 years, around half of people with relapsing-remitting MS will go on to develop secondary progressive MS.

In secondary progressive MS, symptoms gradually worsen and there are fewer or no periods of remission.

The least common form of MS is primary progressive MS. In this type, symptoms gradually get worse over time and there are no periods of remission.


There is currently no cure for MS but there are a number of treatments that can help.

Relapsing-remitting MS and secondary progressive MS can be treated with disease-modifying drugs. These are designed to slow the progression of the disease and reduce the number of relapses. But they are not suitable for all people with MS.

For example at the moment, there is no treatment that can slow the progress of primary progressive MS.

There is also a wide range of treatments, including steroid injections and physiotherapy, that can help relieve symptoms and make day-to-day living easier.


MS is known as an autoimmune condition. This is where something goes wrong with the immune system (the body’s defense against infection) and it mistakenly attacks healthy body tissue – in this case, the myelin covering of nerves.

This can cause multiple sections of the brain and spinal column to become damaged and hardened (sclerosis), which can disrupt the nerve signals passing through these areas.

Exactly what causes the immune system to act in this way is unclear, but most experts think a combination of genetic and environmental factors are involved.

Who is affected

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

Symptoms usually first develop between the ages of 15 and 45, with the average age of diagnosis being about 30.

For reasons that are unclear, MS is twice as common in women than men and more common in white people than black and Asian people


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 disease.

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

As a result, the average life expectancy for people with MS is around 10 years lower than the population at large.

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