Multiple sclerosis

What it is

MS is an immune-mediated disease of the central nervous system, which consists of the brain, spinal cord and optic nerves. The immune system, which normally protects against infection, mistakenly attacks myelin and also damages nerve fibres and nerve cells themselves^2,5.

Symptoms usually begin in young adults, typically between the ages of 20 and 40². The estimated number of people living with MS has risen in every world region since 2013¹.

Many disease-modifying treatments are now available, and the outlook for people diagnosed today is considerably better than in the past^2,4.

SideFrontAbove

White matter around the ventriclesOptic nervesBrainstem and cerebellumGrey matter of the cortex

Lesions, where myelin has been stripped from nerve fibres, are typically seen on MRI in the white matter next to the ventricles and in other characteristic places^5,6.

Inflammation of the optic nerve (optic neuritis) is a common first episode⁵, and the optic nerve now counts as a site of disease in the diagnostic criteria⁷. The highlighted region marks where the two optic nerves meet.

Lesions in the brainstem and cerebellum are among the characteristic sites used in diagnosis⁶. The spinal cord, also often affected, lies below this image⁵.

Damage is not limited to myelin: nerve cells are lost, including in the grey matter of the brain^2,5.

Signs and symptoms

Symptoms depend on which parts of the nervous system are affected and differ widely between people³. Many people first experience an episode lasting days or weeks, such as inflammation of the optic nerve (optic neuritis) or numbness affecting part of the body⁵. Symptoms often worsen temporarily with heat, fever or infection².

• Fatigue, physical or mental, which is very common^2,3
• Blurred vision, eye pain or double vision^2,3
• Numbness or tingling in parts of the body³
• Muscle weakness, stiffness and spasms, and difficulty walking^2,3
• Problems with balance, coordination and dizziness^2,3
• Bladder and bowel problems^2,3
• Changes in memory, concentration and mood, including depression²

Causes and risk factors

The cause of MS is not fully understood. It is thought to arise from an interaction between genetic susceptibility and environmental exposures⁴. Strong evidence now implicates infection with Epstein-Barr virus (EBV), a very common virus that causes glandular fever, although most people infected with EBV never develop MS^2,8.

• Previous EBV infection: in a study of more than 10 million US military personnel, MS risk rose about 32-fold after infection with EBV but not after other viruses⁸
• Female sex^1,3
• Having a parent, brother or sister with MS³
• Smoking, which is linked to a higher risk and a more aggressive course^2,3
• Low sunlight exposure and low vitamin D levels, and living further from the equator²
• Genetic variants affecting the immune system⁹

Genetics

MS is not inherited in a simple way, and no single gene causes it. Instead, many common genetic variants each add a small amount to a person’s risk.

A genetic study of more than 47,000 people with MS and 68,000 controls mapped 233 susceptibility variants, including 32 within the major histocompatibility complex, a gene region that controls how the immune system recognises foreign material⁹.

The genes implicated point to many parts of the immune system and to microglia, the brain’s resident immune cells. This supports the view that MS is triggered by changes in immune responses outside the brain that are then directed at the central nervous system⁹.

What happens in the brain

In MS, immune cells cross into the central nervous system and cause areas of inflammation that strip myelin from nerve fibres. These areas, called lesions or plaques, slow or block electrical signals along the nerves^2,5.

Damage is not limited to myelin. Nerve fibres are cut and nerve cells are lost, including in the grey matter of the brain, and this neurodegeneration is thought to underlie much of the long-term disability^2,5.

Disability can accumulate gradually even without relapses. This is partly attributed to chronic, smouldering inflammation within the central nervous system involving microglia and other immune cells, which current treatments only partly address¹¹.

How it is diagnosed

There is no single test for MS³. A neurologist combines the history and examination with MRI and laboratory findings, using internationally agreed criteria known as the McDonald criteria^5,6. These were revised in 2024 to allow earlier diagnosis while maintaining accuracy, for example by counting the optic nerve as a site of disease⁷.

• Neurological examination of movement, coordination, vision, balance and reflexes³
• MRI of the brain and spinal cord to show lesions in different places and at different times^5,6
• Lumbar puncture to examine cerebrospinal fluid for oligoclonal bands, antibodies made within the nervous system^5,6
• Newer supporting markers such as the central vein sign on MRI and kappa free light chains in cerebrospinal fluid⁷
• Optical coherence tomography (a scan of the retina) or visual evoked potentials to detect optic nerve involvement^2,7
• Blood tests to exclude other conditions that can look like MS³

How scientists study it

Current treatments

Research frontiers

Living with the condition and seeking help

MS affects people very differently; some have mild symptoms with little disability, while others accumulate disability over time². Regular follow-up with an MS team allows treatment to be adjusted to individual needs.

Staying physically active, not smoking, and managing other health conditions can support wellbeing. Support may include fatigue management, mobility aids, home adaptations and psychological therapy³.

Anyone who develops sudden weakness or numbness in one arm, sudden loss of vision or sudden problems with balance should seek emergency care, as these can also be signs of a stroke³. In India, the national emergency number is 112 and the ambulance number is 108^15,16.