Multiple sclerosis is a disease of the brain and spinal cord, known as the central nervous system. The protective coating that surrounds nerve fibers is attacked by the body's immune system, resulting in scars called lesions or plaques.

This damage affects the ability of electrical signals to travel along nerve fibers to and from the brain. The damage causes symptoms that can vary widely depending on which area of the body is affected, and the extent of damage caused.

Scientists do not yet know what triggers the immune system to attack the brain and spinal cord in people with multiple sclerosis (MS). It is thought that a combination of genetic and environmental factors may play a role.

The Multiple Sclerosis International Federation estimate that around 2.3 million people worldwide have MS, which typically develops between the ages of 20 and 40 years.

MS is one of the most common disorders to affect the brain and spinal cord in adults. However, it can also develop in younger and older people. MS is also up to three times more common in women than men, although researchers do not yet know why.

Because MS is such a complex disease, there is no particular set of symptoms associated with the development of the disorder. Indeed, one person with the disorder may have a completely different set of symptoms to another. Nevertheless, some symptoms are more common than others.

The most common symptoms associated with MS include:

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Common symptoms of multiple sclerosis include numbness, weakness, and partial loss of vision.
  • Fatigue
  • Pain
  • Weakness
  • Balance problems and dizziness
  • Stiffness and muscle spasms
  • Numbness and tingling sensations in the muscles
  • Vision problems
  • Poor bladder and bowel control
  • Memory and attention problems
  • Mood swings, depression, and other emotional changes
  • Sexual problems

Of these, the most common first symptoms are numbness and tingling sensations in the arms, legs or face, weakness or poor control of an arm or leg, and partial vision loss or pain in one eye.

People with MS will start to experience such symptoms when damage to the coating of nerve fibers becomes severe enough to disrupt the nerve's ability to send signals.

Less common symptoms include:

  • Speech difficulties
  • Tremors
  • Breathing difficulties
  • Swallowing problems
  • Seizures
  • Hearing loss
  • Itching

Although up to three times more women are affected by MS than men, there are no significant gender differences in the type of symptoms experienced.

However, some women find that their symptoms can get worse during certain periods of their menstrual cycle. This suggests that both hormones and body temperature could play a role in how severe MS symptoms are.

Researchers have also found that pregnant women with the relapsing-remitting type of MS often experience remission during the 3 months before birth when their levels of the hormone estrogen are high. Women then often relapse after giving birth when their levels of the hormone fall.

A recent study published in The Lancet Neurology indicated that estriol, a type of estrogen, can help reduce relapse rates in women with MS.

In addition, study results published in the Multiple Sclerosis Journal in 2014 suggested that low blood levels of the hormone testosterone are associated with an increased risk of disability among men with MS.

Results from another study, published 2014 in the journal NeuroImage: Clinical, indicated "the potential of testosterone treatment to stall (and perhaps even reverse) neurodegeneration associated with MS," according to the authors.

Although each person with MS will experience an individual array of symptoms, researchers have identified several distinct patterns of the disease's course:

Relapsing-remitting disease pattern

People with this common pattern of MS experience unpredictable symptom attacks (relapses) that can last for short or extended periods followed by periods in which the disease is inactive (remission).

Primary progressive disease pattern

This pattern of disease, which affects around 15 percent of people with MS, is distinguished by a slow worsening of symptoms without relapses or remissions. There may be temporary periods in which symptoms do not worsen, however.

This type of MS is usually diagnosed after the age of 40 years and is the only type to affect women and men equally.

Secondary progressive disease pattern

This pattern of disease occurs in people who initially have relapsing-remitting MS and then develop a gradual worsening of symptoms.

Progressive relapsing disease pattern

People with this rare type of disease pattern experience a gradual worsening of symptoms with periods of relapses but no remissions.

However, in a 2014 article published in the journal Neurology, experts suggested changes to these definitions of MS types, to account for better ways of monitoring the disease. They suggested classifying MS based on disease activity seen in magnetic resonance imaging (MRI) brain scans.

For example, someone who showed new areas of nerve damage might be defined as having a "relapsing remitting-active" pattern. Another patient with scan results that remained largely the same might be defined as having a "relapsing remitting-non-active" pattern.

They also suggested that the progressive relapsing pattern should be reclassified as "progressive multiple sclerosis-active," and that a person's first episode of neurological symptoms (clinically isolated syndrome) should be classed as a type of MS.

MS is difficult to diagnose in its early stages because symptoms such as numbness, tiredness, or muscle stiffness are often vague and can occasionally occur over months or years.

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Doctors diagnose cases of multiple sclerosis using specific criteria.

These types of symptoms can also be associated with a variety of other conditions. As a result, strict criteria called the revised McDonald Criteria are most commonly used to diagnose the condition.

To make a diagnosis of MS using these criteria, a doctor should ensure that:

  • At least two different areas of the central nervous system are affected
  • Symptoms have been experienced by the patient on at least two separate occasions at least 1 month apart, and evidence of nerve fiber damage is shown by MRI scanning
  • All other possible causes have been ruled out

The revised McDonald Criteria were published in 2010 by the International Panel on the Diagnosis of Multiple Sclerosis. These criteria also include guidelines for using MRI scanning, examining fluid in the brain and spine, and other tests to speed up the diagnosis.

Several conditions can show symptoms similar to those caused by MS. These conditions must be ruled out by a doctor, and include:

  • Infections of the central nervous system, such as Lyme disease, HIV, and syphilis
  • Central nervous system inflammatory disorders, including Sjögren's syndrome, vasculitis, lupus, sarcoidosis, and Behçet's disease
  • Brain tumors
  • Copper and vitamin B12 deficiencies
  • Damage in the brain or spinal cord, such as cervical spondylosis, herniated disc, and Chiari's malformation
  • Genetic disorders, including hereditary cerebellar degeneration, mitochondrial disease, and leukodystrophies
  • Other disorders that damage the coating of nerve fibers, including neuromyelitis optica, and acute disseminated encephalomyelitis

There is currently no known cure for MS. However, a number of treatments have been developed that can change the course of the disease. Many of the symptoms can also be effectively managed.

Managing MS often involves a combination of treatments that depends on the symptoms experienced by an individual.

Disease-modifying therapies can help reduce the number of relapses among people who experience them, and may also slow the progressive damage caused by the disease.

High doses of drugs called corticosteroids often prove effective at reducing the inflammation associated with severe symptoms. Doing so can shorten the time of relapses. However, there is no evidence to suggest that steroids affect the long-term outlook of MS.

People with MS also find that exercise and maintaining a healthy lifestyle can help combat some of the symptoms of the condition, such as fatigue, muscle problems, depression, and mood swings.