Overview
Multiple sclerosis (MS) is a chronic autoimmune disease in which the immune system attacks the myelin sheath protecting nerve fibres in the brain and spinal cord, disrupting electrical signals. MS can cause a wide range of neurological symptoms. It follows a relapsing-remitting course in 85% of patients at onset. It is a leading cause of disability in young adults.
How common is it?
A 2024 MS Society study estimated that more than 150,000 people live with MS in the UK. It is more common in women, with diagnosis often in the 30s and 40s.
Causes and risk factors
MS results from immune-mediated demyelination triggered by environmental exposures in genetically susceptible individuals. The precise autoantigen is not fully established.
Common risk factors
- Genetic susceptibility (HLA-DRB1*15:01 allele; highest risk but not deterministic)
- Epstein-Barr virus infection (strong and causal association — almost all MS patients have had EBV)
- Low vitamin D levels (inverse association)
- Smoking (increases risk and worsens progression)
- Latitude and UV light exposure (higher prevalence further from equator)
- Childhood obesity
- Female sex
Symptoms
- Optic neuritis: painful loss of vision in one eye (common first presentation)
- Limb weakness and fatigue
- Sensory disturbance: numbness, tingling, electric shock sensation on neck flexion (Lhermitte sign)
- Balance and coordination problems (ataxia)
- Bladder dysfunction: urgency, frequency, incomplete emptying
- Cognitive impairment and brain fog
- Depression and anxiety
- Sexual dysfunction
- Spasticity and muscle stiffness
- Fatigue — the most common and disabling symptom
When to see a doctor
Call emergency services (999 in the UK) for sudden weakness or numbness, new speech difficulty, sudden vision loss or major balance problems. These may be signs of a stroke, even in someone with multiple sclerosis. Do not wait 24 hours or drive yourself. Arrange assessment for other new or persistent symptoms, and contact your MS team about possible changes in an established condition.
Diagnosis
A neurologist combines symptoms and examination with MRI and, when needed, spinal fluid or visual pathway tests. The revised 2024 McDonald criteria, published in 2025, guide diagnosis while other causes are excluded.
Treatments
Disease-modifying therapies (DMTs)
Injectable, oral and infusion disease-modifying treatments can reduce relapses and slow disability in eligible people. Selection depends on MS type, activity, infection risks and pregnancy plans. Alemtuzumab has restricted indications and requires enhanced monitoring for serious adverse effects.
Acute relapse management
A clinician may prescribe high-dose methylprednisolone for a relapse that affects usual activities, after checking for infection and other causes. Steroids can speed recovery but do not change long-term progression. They can raise glucose; people with diabetes need a monitoring plan.
Symptom management
Treatment is tailored to spasticity, bladder symptoms, mood and fatigue. A specialist may consider amantadine, modafinil or an SSRI for fatigue after discussing limits and risks. Modafinil is not for pregnancy or planned pregnancy and can reduce hormonal contraceptive effectiveness. Fampridine is not a fatigue treatment.
Autologous haematopoietic stem cell transplant (AHSCT)
AHSCT uses chemotherapy followed by the person's own blood-forming stem cells. It may help carefully selected people with highly active relapsing MS but has serious risks, including infection and effects on fertility. Access depends on specialist assessment and local commissioning criteria.
Self-care and lifestyle
- Get support to stop smoking; smoking is associated with worse MS outcomes.
- Discuss vitamin D intake and any deficiency with your care team; do not use high-dose supplements as a substitute for MS treatment.
- Regular aerobic and resistance exercise improves fatigue, mobility, and cognition in MS
- Cooling strategies for heat-sensitive symptoms (Uhthoff phenomenon)
Prevention
No reliable prevention is established. Vitamin D sufficiency and avoidance of smoking from early life may reduce risk.
Sources for targeted updates
Updated: 24 October 2026. Targeted corrections to frequency, diagnosis, treatment, self-care, key facts. This update covers the named sections; a full review of the remaining guide is pending.