Multiple sclerosis (MS) is an autoimmune disease that affects the central nervous system (CNS). In MS, the immune system attacks the fatty coating on nerve cells, resulting in nerve damage. There are four main types of MS that differ in their progression and symptoms. Understanding what MS is, how it develops, and the symptoms you may experience can help you learn how to manage the disease.
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Who Develops MS?
MS can affect anyone, but it’s most likely to develop in people between the ages of 20 and 50. There are some cases where MS develops in children and older individuals as well. Interestingly, women are three times as likely to develop MS compared to men — leading researchers to believe that female sex hormones may play a role in the disease. Almost 1 million people in the United States are living with MS — almost double what was previously estimated.1
Race and ethnicity also play a role in who develops MS. The condition is most common in White people with northern European ancestry. Studies show that people who live in northern latitudes are also more likely to develop MS. However, the condition can also develop in people of Hispanic, African American, or Asian descent. Recent research has found that MS may affect more African Americans than was previously thought.2
What Causes MS?
Researchers aren’t quite sure of exactly what causes MS, but they believe it’s a combination of a person’s genetics, immune system, and previous viral infections.
Genetics and MS
Unlike many other diseases, MS is not inherited (passed down through family members). Instead, a person may have a mutation in a gene that increases their risk of developing MS. Researchers have found around 200 different genes that may contribute to a person’s risk.3
Having family members with MS does increase your chances of developing it yourself. This is primarily seen in identical twins — if one twin has MS, there is a 25 percent chance that the other twin will develop it as well. Having parents or siblings with MS also increases your chances, but much less than if you have an identical twin.3
The Immune System and MS
In people with MS, the immune system is dysregulated and accidentally mistakes the body’s own tissues as foreign invaders.
The immune system contains many different cells, and two important types in MS are T cells and B cells. Activated T cells make their way to the central nervous system, where they begin creating inflammation by releasing signaling molecules known as cytokines. This brings in more immune cells that attack and damage the fatty coating (known as myelin) that covers nerve cells, in addition to the cells that make myelin and the nerves themselves. This results in nerve damage that leads to MS symptoms.3,4
The T cells also activate B cells, which are responsible for making antibodies. In MS, B cells make antibodies that bind to myelin and tag it for destruction by the immune system. Almost 95 percent of people with MS have antibodies in their cerebrospinal fluid (CSF) that are known as oligoclonal immunoglobulin bands (OGBs).5
Viral Infections and MS
Researchers believe that infections with certain viruses may also trigger MS. Viruses that have been studied for their role in MS include:3
- Epstein-Barr virus (EBV)
- Human herpesvirus-6
- Chlamydia pneumonia
A study published in January 2022 found very strong evidence that EBV triggers the development of MS. Around 95 percent of adults will be infected with EBV at some point in their lifetime, but very few will go on to develop MS. Interestingly, researchers found that out of the 801 participants from the study, 800 of them tested positive for EBV before they developed MS. People who have been infected with EBV are 32 times more likely to develop MS than uninfected individuals.6
Risk Factors for MS
Having certain risk factors can also increase your risk of developing MS. These include having low vitamin D levels, living in a specific geographic location, obesity, and smoking.
Low Vitamin D Levels
Vitamin D is an important vitamin that helps your body absorb and use calcium. Together, these nutrients help maintain bone and muscle health. When your skin is exposed to sunlight, your body makes its own vitamin D. Vitamin D can also be found in milk, fatty fish, and fortified cereals.7 Studies have found that low vitamin D levels are associated with an increased risk of MS. Researchers believe that vitamin D promotes immune system function — as a result, low levels may cause the dysfunction seen in MS.
Your geographic location can also play a role in your risk of developing MS. People who live in northern latitudes are more likely to develop MS. Some researchers think this may be linked to vitamin D levels since people who live in northern countries tend to get less sunlight than those living closer to the equator.8
Researchers have found that obesity can significantly increase the risk of developing MS later in life. Studies have found that obesity in women during early adulthood increases the risk of MS by 2 to 2.25 times compared to those with a body mass index (BMI) in the normal range.9 Childhood obesity in girls has also been linked to an increased risk of MS.3
People who smoke are also more likely to develop MS. Researchers believe that smoking increases inflammation in the body and has a direct impact on immune cells. Studies show that smoking not only increases your risk of MS, but it may also be associated with more severe symptoms and quicker disease progression. People who stop smoking either before or after an MS diagnosis are able to slow their disease progression.3,10
Diabetes affects the body’s ability to produce and/or use insulin properly. People with type 1 diabetes (T1D) — an autoimmune disease in which the pancreas can’t make insulin — is a risk factor for developing MS. Research shows that people with T1D are three times as likely to develop MS than those without.11
Types of MS
There are four main types of MS that are broken down by the patterns of attacks (relapses) and recovery (remissions). These include clinically isolated syndrome, primary progressive MS, secondary progressive MS, and relapsing-remitting MS. MS is generally characterized by relapses, or worsening or flares of symptoms. Disability refers to neurological symptoms, such as difficulty walking, muscle weakness, or spasms.
Clinically Isolated Syndrome
Clinically isolated syndrome (CIS) refers to the first time you may experience MS-like symptoms. These symptoms have to last for at least 24 hours to be considered CIS. You may experience only one symptom (known as a monofocal episode), or you may have multiple symptoms (known as a multifocal episode). CIS is caused by loss of myelin or inflammation in the central nervous system.
If you develop CIS, it doesn’t necessarily mean you’ll develop MS. People with CIS who are at a high risk of developing MS have scarring — or lesions — on their brain that can be seen with magnetic resonance imaging (MRI). Having these lesions increases a person’s risk of having a second bout of CIS symptoms or developing MS to between 60 and 80 percent. On the other hand, people without brain lesions have only a 20 percent chance of developing MS.12
Relapsing-remitting MS (RRMS) is the most common form of MS. Around 85 percent of people with MS are first diagnosed with this form. RRMS is diagnosed when a person experiences clear relapses — attacks in which neurologic symptoms worsen — and periods of remission — partial or complete recovery from symptoms. During relapses, the immune system is actively attacking myelin in the CNS, resulting in MS symptoms.13
RRMS is defined by periods of:
- Relapse, in which new or returning MS symptoms become worse
- Active disease with relapses and/or new lesions found by MRI, but with no increase in disability
- Worsening — or an increase in — disability after a relapse
- Stable disease with no relapses and/or new lesions, but with an increase in disability
- Remission with partial or complete recovery from symptoms and no disease progression
RRMS typically involves more inflammatory lesions often found in the brain. Diagnosis of RRMS is more common in younger people between the ages of 20 to 30.13
Primary Progressive MS
Primary progressive MS (PPMS) is a form of MS characterized by the worsening of disease and disability after symptoms first begin. There are no periods of remission in PPMS. Instead, it continues to progress over time, with periods of:14
- Active disease (relapses or new lesions found on MRI) with progression (increase in disability)
- Active disease without progression
- Non-active disease (no new relapses or lesions) with progression
- Non-active disease without progression (stable disease)
PPMS differs from other types of MS in that there is less inflammation, meaning that people with this disease often have fewer brain lesions. However, they do have more lesions on their spinal cord. As a result, those with PPMS have more trouble walking than those with relapsing forms of MS. While RRMS tends to affect women more than men, PPMS occurs equally in both.14
Secondary Progressive MS
Secondary progressive MS (SPMS) initially looks similar to RRMS, but it eventually progresses to the secondary form. SPMS is characterized by the worsening of neurological symptoms over time, which results in more significant disability. Like PPMS, SPMS can also be defined by periods of active disease (relapses and new lesions found on MRI scans) or non-active disease (remission), along with progression (worsening of symptoms and disability) or without progression.15
SPMS typically develops over time in people who were originally diagnosed with RRMS. In the beginning, you may experience some relapses similar to RRMS. However, as SPMS progresses, the nerves become more damaged, eventually leading to nerve loss.15
Symptoms of MS
Every person’s experience with MS is different, and symptoms of the disease vary from person to person. These symptoms fluctuate over time, as MS is defined by periods of relapses and remissions. Generally, MS symptoms include:16
- Fatigue — around 80 percent of people with MS report this symptom, which largely interferes with everyday life
- Tingling or numbness in the arms, legs, or face — often one of the first MS symptoms people experience
- Vision problems — includes blurred vision or pain when moving the eyes
- Muscle weakness — the result of nerve damage and not using muscles as often
- Spasticity — involuntary muscle spasms and stiffness that commonly affect the legs
- Difficulties walking (unsteady gait) — related to muscle weakness and spasticity
- MS hug — also known as dysesthesia, which feels like a squeezing sensation around your chest and abdomen
- Bladder issues — occur in around 80 percent of people with MS
- Bowel issues — common in people with MS, particularly constipation
- Lightheadedness or dizziness — may cause you to feel off-balance
- Sexual problems — the result of nerve damage, spasticity, and fatigue
- Cognitive problems — include difficulty learning, processing, and remembering information
Less common symptoms of MS that occur in some people include:16
- Loss of taste — occurs in around 25 percent of people with MS
- Difficulties swallowing (dysphagia) — the result of nerve damage to the muscles in the throat and mouth
- Speech problems — occur in around 25 to 40 percent of people with MS, including loss of volume when speaking (dysphonia) and slurring of speech (dysarthria)
- Difficulties breathing — the result of weak chest muscles caused by nerve damage
- Seizures — occur in between 2 to 5 percent of people with MS, caused by scarring/lesions in the brain and abnormal electrical activity
- Hearing loss — occurs in around 6 percent of people with MS
- Tremors — uncontrollable shaking as the result of nerve damage
Symptoms of Clinically Isolated Syndrome
Clinically Isolated Syndrome symptoms are specific to the condition and depend on the location of the damaged myelin. This can be in the optic nerve, spinal cord, or brainstem.17
When the optic nerve is damaged, it causes optic neuritis. This results in:
- Eye pain
- Blurry vision
- Loss of vision, typically only in one eye
- Blind spots
- Decreased color vision
Damage to the spinal cord causes transverse myelitis. Symptoms include:
- Numbness or tingling in the arms and legs
- Muscle weakness
- Bowel and bladder problems
- Lhermitte’s symptom — a sensation similar to an electric shock when you move your neck
Symptoms related to brain stem damage include:
- Loss of hearing
- Unsteady gait
- Double vision
How Is MS Diagnosed?
MS can’t be diagnosed through one single test. Instead, a combination of neurological and imaging tests and a spinal tap is used to rule out other conditions and make a final diagnosis.
Your doctor will likely start by taking your medical history, which lets them know if you have any risk factors for developing MS. They may ask about:
- Your specific symptoms and how long they’ve been occurring
- Where you were born
- Your family’s medical history (whether anyone else has MS)
- Past infections or exposure to toxins
A neurological exam tests how well your nervous system is functioning. Your doctor will check your coordination, balance, eyes, and reflexes for signs of nerve damage.
To test your balance and motor function, your doctor will have you push and pull against them or stand with your eyes closed to try and balance yourself. They may also perform a sensory test, which checks your ability to feel sensations on the skin. Your doctor will touch different parts of your body with dull or sharp objects, and you’ll respond with the sensations you feel. Since MS causes nerve damage, your doctor may see abnormal results in different tests which together may point to a diagnosis.18
Evoked Potential Test
An evoked potential (EP) test measures how quickly your nerves respond to stimulation. Patches with electrodes that measure your brain’s electrical activity are placed on your scalp. Your doctor then stimulates different parts of your brain using noises, lights, or tiny electric shocks, and the electrodes record how your brain responds.
Due to the loss of myelin (demyelination) in the nerves, people with MS will have slower responses than those without MS.19
Magnetic Resonance Imaging (MRI)
Magnetic resonance imaging (MRI) is one of the most important tools for diagnosing MS. MRI uses very strong magnets and radio waves to take highly detailed pictures of the brain and spinal cord. Before an MRI, you may also receive an injection with the contrast agent gadolinium, which helps your CNS stand out in pictures.
MRIs are used to look for MS lesions on the brain, spinal cord, and optic nerves in the eyes. Your doctor will use these images to diagnose and track the progression of your MS over time. Even if you’re not experiencing a relapse, your doctor may find new lesions, which shows that your MS is progressing.20
Your doctor may also perform a spinal tap (lumbar puncture) to look for antibodies (OGBs) in the cerebrospinal fluid (CSF) that surrounds your brain and spinal cord. There may also be proteins in the CSF from the breakdown of myelin, which may point to an MS diagnosis. The presence of OGBs and protein in the CSF doesn’t guarantee an MS diagnosis — it simply means that the immune system is attacking the central nervous system. Between five to 10 percent of people with MS don’t have any abnormalities in their CSF.21
Complications from MS
MS causes nerve damage that progresses over time. In some people, this nerve damage becomes permanent, which limits their mobility and organ function. This results in health complications, which include:22-25
- Pressure sores or bed sores that develop from sitting or lying down for extended periods of time
- Urinary tract infections from loss of bladder control and function
- Osteoporosis (loss of bone density) due to inactivity
- Mental health conditions, including anxiety and depression
- Trouble walking, which may eventually lead to needing a walker, cane, or wheelchair
Resources for Living With MS
If you’re living with MS, there are many resources from hospitals and foundations to help guide you through diagnosis, treatment, and living with MS.