Multiple sclerosis (MS) is a highly complex and unpredictable disease that affects people differently. In MS, the immune system attacks the nervous system, and over time the immune system wears down the protective cover on the nerves. This damage is called sclerosis. In fact, the term multiple sclerosis means “many scars.”

This section provides some history and basic explanations and explores how MS affects the body's nervous system.

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Age, gender & nationality

Although MS can occur at any age, it is commonly diagnosed between the ages of 20 to 40, although onset may be earlier.

Reference: Multiple Sclerosis Society of Canada (MSSC),

MS is three times as likely to occur in women than in men.

Reference: Multiple Sclerosis Society of Canada (MSSC),

It is estimated that MS affects more than two million people worldwide, most commonly people of Northern European background. Canada is known to have one of the highest rates of MS in the world, currently affecting approximately 100,000 Canadians.  

Reference: Multiple Sclerosis International Federation,

MS and the body

MS is an autoimmune disease of the central nervous system (CNS) and its course and symptoms vary from person to person.

MS causes inflammation or swelling around small blood vessels in the brain and spinal cord, and leads to the formation of damaged areas on the surface of the brain called “lesions.”  This inflammation appears to be caused by the immune system, which normally protects the body against viruses, bacteria and other biological invaders. Although MS can occur at any age, it is commonly diagnosed between the ages of 20 to 40, although onset may be earlier.  


In individuals with MS, white blood cells are able to leave the circulatory system and enter the nervous system, where they are not supposed to be.


When white blood cells encounter the nerve cells in the body or in the brain, they may attack the protective covering of nerve fibres outside of the nerve, an area called the myelin sheath.



The inflammation and damage of myelin and nerve fibres that occur in MS weaken the transmission of nerve impulses sent between the brain, the spinal cord and the rest of the body.

When the brain cannot communicate with the nerves and muscles the way it is supposed to, various symptoms of MS (such as vision problems and difficulty with muscle movement, coordination, and balance) can occur. 

The complex nature of MS

Despite a great deal of research, scientists have not yet pinpointed the exact cause(s) of MS. However, the best current evidence suggests that a combination of lifestyle , environmental , genetic and biological factors all contribute. 


While it is not hereditary, MS does appear
to be genetic to some extent. 

  • The risk of developing MS is low for the general population. For family members of a person confirmed to have MS, the risk is about 1% to 3%. 
  • Some researchers speculate that MS develops because a person is born with a genetic tendency to react to some environmental agent that, upon exposure, triggers an immune-mediated response. 
  • Studies have shown that there is a higher prevalence of certain genes in populations with higher rates of MS. Common genetic factors have also been found in some families where there is more than one person with MS. 


A great deal of research has investigated the links between MS and many kinds of viruses.  

  • MS is not contagious, but the possibility of a virus triggering the disease cannot be ruled out. 
  • To date, researchers have not been able to identify a single virus as the trigger for MS. Several viruses have been studied, but multiple steps are required in order to show that a particular virus causes MS. 
  • Researchers must prove that the virus is in the body before MS develops, and the virus actually causes the disease and is not just happening alongside the disease.
  • A likely possibility is that MS only develops in people with certain genetic codes that put them at risk, but the onset of the disease itself is a response to outside factors.


Climate may play a role in the development of MS. 

  • MS most commonly affects Caucasians, particularly in North America, Europe and Australia. 
  • Growing evidence suggests that vitamin D plays an important role. Vitamin D is thought to support the immune function and may help protect against immune-mediated diseases like MS.
  • People living closer to the equator are exposed to greater amounts of sunlight year-round, and tend to have higher levels of naturally produced vitamin D.

The 4 types of MS and how they may affect the body

With MS, the course of illness and range of symptoms can vary from person to person, but there are very different types of the disease. Some are considered “relapsing” types of MS, while others are considered “progressive.”

With the relapsing types of MS, people will experience periods of visible disease activity (relapses) alternating with periods of remission or recovery. Others will experience only a gradual and steady progression of disability, called progressive MS.

There are four types of MS and a condition known as “clinically isolated syndrome” (CIS)

Clinically isolated syndrome (CIS)

When a person has experienced a single episode of MS-like symptoms, there may not be enough evidence for a complete diagnosis of MS.

  • This is called clinically isolated syndrome (CIS), and it is typically the first stage of MS.
  • Treatment can begin at this stage, before another event occurs, in order to delay the progression of MS.

Relapsing-remitting MS

Relapsing-remitting MS (RRMS) is the most common type of MS and is most commonly seen when people are first diagnosed.

  • This type shows clearly defined relapses with some amount of recovery. It affects around 85% of all people with MS.
  • There are acute (short-term) relapses (attacks of symptoms) followed by recovery between relapses. The amount of recovery varies – some people may have full recovery between relapses, while others have only partial recovery.
  • Relapses may last for anywhere from days to months.
  • About half of people with RRMS will develop “secondary progressive MS” within 10 to 20 years.

Secondary progressive MS

It is estimated that about one third of people with MS have this type of the disease.

  • While technically a type of progressive MS, secondary progressive MS acts more like a relapsing type of MS in its early-to-mid stage, with relapses and remissions being quite common.
  • Eventually a more continuous loss of physical and cognitive functions starts to take over, and relapses become less common.
  • Roughly two thirds of people with secondary progressive MS have relapses and thus also fall within the definition of relapsing MS. 

Primary progressive MS

This type of MS affects about 10% of all people with MS and is the most common type of MS in people diagnosed after age 40.

  • This type shows no relapses (attacks or flare-ups), but over a period of years, there is steady, gradual loss of physical and cognitive functions.
  • There may be small improvements or plateaus (when the symptoms stay stable), but overall, symptoms tend to get gradually worse.

Progressive-relapsing MS

PRMS is the least common of the four MS disease stage.

  • Approximately 5% to 10% of people with MS have this type of the disease.
  • This type of MS has relapses (attacks or flare-ups) but also steadily gets worse between relapses.
  • People with this form of MS may or may not experience some recovery following these attacks – the disease continues to progress without remissions.
  • Although PRMS is progressive from the onset, each person’s symptoms and rate of progression will be different.

Progression of MS

The brain and spinal cord make up the central nervous system (CNS). From the CNS, nerves extend throughout the body to make up the peripheral nervous system. Significantly, MS affects only the CNS.

Here is a closer look at the complexity of the CNS and how it might be affected by MS:


Essentially, the CNS is a big processing centre that helps coordinate activity in all parts of the body:   

● Walking

● Speaking

● Balance

● Vision

● Memory

● Eye and muscle control


  • Nerve cells and fibres are the building blocks of the CNS.
  • These cells communicate with other parts of the body via tiny electric signals.
  • These signals travel along the nerve fibres (also called axons) to other parts of the body.
  • Much in the way telephone signals travel along a phone wire, this messaging process is repeated in billions of locations in each person’s nervous system, all day, every day.
  • The myelin sheath insulates and protects axons and helps signals travel efficiently to and from the brain, telling the body what to do.

  • The myelin protein gets damaged in MS, and the damage is known as demyelination, which is why MS is called a demyelinating disease.

The immune system and MS

  • The immune system works on the premise that there are “self” tissues – which are of the body – and “nonself” tissues, which are not.
  • The immune system does not tolerate “nonself” or foreign tissues and relentlessly tries to destroy them.
  • For reasons unknown, the immune system attacks the body’s own myelin sporadically in MS.
  • The location and intensity of the attacks are unpredictable, and vary greatly not only within a person but from one person to the next.

    *In general, a person’s symptoms mirror the extent of the myelin damage.  

Understanding the impact of MS


In early MS, your brain will usually repair all of the damage caused by a relapse (also referred to as an “attack” or “flare-up”). As MS progresses, the brain can repair most of the damage, but not all. Because of this incomplete recovery, leftover symptoms accumulate and disability progresses.

  • When someone experiences a relapse (attack or flare-up), it means the MS is active.
  • The symptoms experienced from relapse are due to the damage caused to the CNS (central nervous system); this damaged area is called a lesion.

  • Relapses are characterized by the development of new MS symptoms and/or the worsening of a problem a person may already have.
  • The symptoms one may experience will depend on the part of the CNS that has been damaged and the severity of the damage.

Exploring how MS progresses over time

The symptoms of MS become worse over time as more nerves become damaged.

The progression of MS varies depending on how much nerve damage there is, how quickly it happens and where it occurs. Research shows that MS continues to progress, even when a person is not having relapses. This happens because MS has two components: the invisible disease and the visible results of it.

The invisible aspect of MS is the ongoing inflammation in the brain and spinal cord, causing scarring and loss of nerve tissue, which leads to the visible effects of MS:

●     Relapses: temporary episodes of problems with walking, speech or vision

●     Physical disability: sensory, motor or other neurological problems that persist or continue to progress

●     Cognitive dysfunction: problems with memory and other thinking skills

The progression of MS varies depending on how much nerve damage there is, how quickly it happens and where it occurs. Research shows that MS continues to progress, even when a person is not having relapses. This happens because MS has two components: the invisible disease and the visible results of it.

The graph BELOW illustrates the importance of early treatment

If left untreated, MS progresses and can become more disabling. It moves into another stage, called secondary progressive MS.

When this happens, a person’s level of disability steadily increases, without periods of relapse and remission. The damage to the nervous system worsens and symptoms become more limiting when MS is untreated.

  • It is very important to treat MS as early as possible, even if the disease is in the invisible phase, to slow the progression of disability.
  • Treating early can help slow the disease, preventing damage from occurring as quickly.
  • Medicines using interferon have been proven to slow the progression of disability in relapsing-remitting and secondary progressive MS.

Reference: Kremenchutzky M et al. The natural history of multiple sclerosis: a geographically based study 9: Observations on the progressive phase of the disease. Brain. 2006; 129: 584-594.

History of MS

Drawings from autopsies (thorough examinations of corpses to determine the cause and manner of death) done as early as 1838 clearly show what we now recognize as MS. In 1868, Jean-Martin Charcot, a professor at the University of Paris who has been called “the father of neurology,” outlined a condition called “la sclérose en plaques” – in effect, multiple sclerosis. Charcot wrote a complete description of the disease and the changes in the brain that accompany it, having identified the condition’s gradual development in a maid employed in his house.


Charcot’s further scientific exploration of MS paralleled the creation of neurology, the specialty branch of medicine that deals with diseases of the nervous system. In those early days, the only way to determine what was going on in a person was through neurological examination –that is, by having the person demonstrate how well certain functions of the nervous system (vision, balance, reflexes and so on) were working.

In the time since Charcot's initial research, many new discoveries have helped medical professionals better understand and treat MS. New advancements continue to provide insight into better therapeutic treatments and help shape the medical community's awareness of MS.


1920-1930: Early discoveries

 In the decade after World War I, research grew more sophisticated

  • Abnormalities in spinal fluid noted for the first time in 1919
  • Cells that make myelin (oligodendrocytes) were discovered in 1928
  • Dr. Thomas Rivers at the Rockefeller Institute in NYC demonstrated that immune cells, not viruses, produced the MS-like illness in the 1930s

It would be many years before a link between the immune system and MS was forged

1940-1950: Myelin composition

WWII focused energies of the scientific world on new technologies

  • 1943: the actual composition of myelin was determined
  • 1946: National Multiple Sclerosis Society was founded. It was formed to promote contacts among neurologists around the United States who treated MS and to raise money to fund a search for answers

Research into every aspect of MS ranged from description and diagnosis to causes and cures

1950-1960: DNA structure

  • Geographical gradient discovered: incidence and prevalence of MS increased steadily as one moved northward away from equator
  • Doctors who treated people with MS in the 1950s continued to suspect the cause lay in impaired blood flow – circulation stimulators dominated treatment
  • Nobel Prize-winning description of DNA structure by Francis Crick and James Watson allows for clearer understanding of the way in which genes control biologic functions – including how the immune system is regulated by sequences of genes
  • Myelin was further broken down – scientists studied B-cells, T-cells, genes and myelin but without uncovering a clear unifying threat to direct MS treatment

Treatments were still based more on opinions than facts

1960-1970: The immune system

  • National MS Society had established 114 chapters
  • NMSS funds a panel of experts, headed by Dr. George Schumacher, to draw up standard guidelines for MS diagnosis
  • Rating scale developed by Dr. John Kurtzke to determine the level of disability and the parts of the nervous system affected by MS

Thanks to the ability to make accurate diagnosis and measure how therapies affected disability, it became possible to begin scientifically testing MS treatments

Scientific research points to two big ideas that:

  1. Led scientists to consider the possibility that MS involves a direct immune-system attack on myelin
  2. Revived older thinking that MS could be caused by a virus – but was now thought to alter the immune system and trigger it to  damage myelin

Both ideas remain closely tied today: MS may combine features of both an infectious and an autoimmune disease

1970-1980: Laboratory advances

  • First CAT scans (X-ray test in which a computer generates cross-section views of a patient’s anatomy) performed on people with MS in 1978
  • Diagnosis of MS improved with introduction of brain wave tests called “evoked potentials” (measures nerve conduction 
    throughout the optic nerves, brain and spinal cord and often detect hidden areas of scarring and damage)
  • Steroids to suppress immune activity now widely used to treat MS attacks
  • First small studies were performed using interferons (c. late-1970 interferon)

1980-1990: MRI diagnosis

Explosion of new drug trials

Guided by the NMSS (National Multiple Sclerosis Society), an organization based in the U.S., scientists reached a consensus on the design and conduct of research for new treatments, and dozens of different therapies were tested in attempts to control or cure MS:

1981: first MRI (magnetic resonance imaging) scans of people with MS performed

1982: MS lesions imaged in living patients

1984: MRI shows it can actually see MS attacks within the brain – including many which did not cause any symptoms

1988: sequential MRI scans changed the entire concept of MS by showing that it is a constant, ongoing disease even though relapses with symptoms may appear only sporadically

  • Determination is made (by way of first studies of identical and fraternal twins) that genes determine only part of the MS risk
  • Features affecting the mind – especially functions of awareness, feelings or motivations) and mental-health issues begin receiving research attention

1990-2000: Treatment breakthroughs

Advances powered by the incredible power of new technology

  • Enhancements to MRI allowed it to detect MS plaques earlier and more accurately leading to more rapid diagnosis of the disease
  • Studies with a series of MRI scans over time showed how MS plaques actually develop and permitted researchers to track the “burden of the disease” (total plaque area) in individual patients
  • MRI scanning gave researchers faster and more sophisticated ways of testing drugs to treat MS allowing the benefits of a new drug to be seen on MRI scan before they can be seen in patients themselves
  • Internet brings faster, better communications and data analysis to MS doctors and researchers from all over the world leading to powerful coalitions
  • Large data bases used to track and analyze thousands of patient histories are created, used to clarify their disease variations and responses to treatment
  • Characteristic patterns of MS begin to emerge
  • Advent of disease-modifying therapies (DMTs)


  • Research reveals many ways in which MS can alter the mind, e.g., slowing down thinking and memory
  • Refinements in rehabilitation, exercise and physical therapy benefit people with MS
  • Years of research with drugs to treat the actual disease--and not just its symptoms came to fruition with: BETASERON® (beta interferon 1-b) in 1995,  AVONEX® (beta interferon 1-a) and REBIF® (beta interferon 1-a) in 1998 and  COPAXONE® (glatiramer acetate) in 2001

MS clinics and research laboratories are now linked, able to share and evaluate new findings.

2000-Present: Treatment advances

By the middle of the 2000s, a new class of drugs called monoclonal  antibodies were introduced, aimed at suppressing relapses of MS.

In 2006, Biogen introduced TYSABRI ® (nataluzimab), Canada’s first monthly infusion treatment.

Since 2011, steady advancements have been made  in the development of MS therapies.

  • 2011: Oral treatment options became available in Canada, beginning with GILENYA® (fingolimod), followed soon thereafter by TECFIDERA® (dimethyl fumarate) and AUBAGIO® (teriflunomide).

  • 2014: LEMTRADA® (alemtuzumab), a new infusion therapy, was launched.
  • 2015: PLEGRIDY®  (peginterferon beta-1a), a newer form of injectable, was introduced.

In 2012 the first treatment for MS-related symptoms was introduced.

  • 2012: FAMPYRA® (fampradine) was made available to help with mobility issues.

Biogen and research

As a leader in MS – both globally and in Canada – Biogen is commited to evolving the understanding of MS treatment. In order to accomplish this, Biogen invests in three ways:  proprietary research, undertaking clinical studies and partnering with third-party researchers.


Much of the material on this website may be new for readers, and as such, an expansive glossary has been created to help define technical terms and concepts. The goal of this glossary is to enhance the understanding of MS and MS-related topics.

See the glossary located within the RESOURCES section


For over 30 years, Biogen has been a leader in MS research and currently offers the broadest MS therapy portfolio to help people with relapsing forms of MS.