Multiple sclerosis (MS) is a chronic inflammatory disease that affects the central nervous system. It damages the myelin sheath that surrounds and protects nerve fibers, leading to communication problems between the brain and body. The cause of MS is still not fully understood, but research suggests it may be related to a combination of genetic and environmental factors. Some theories have proposed that MS may be triggered by a pathogen, such as a virus or parasite, but there is no definitive evidence to support this.
What causes MS?
The exact cause of MS is unknown, but experts believe it is likely caused by a combination of genetic susceptibility and exposure to some kind of environmental trigger. Some of the factors that may play a role include:
- Genetics: MS is not directly inherited, but having a close family member with MS does increase your risk. Certain genes may make people more susceptible.
- Environmental triggers: Potential triggers that have been studied include viral infections, vitamin D deficiency, and smoking.
- Immune system: MS is believed to be an autoimmune disorder, meaning the body’s immune system mistakenly attacks the myelin sheath.
- Age: MS most often initially appears between ages 20 and 40.
- Geography: MS is more common in certain parts of the world, including Northern Europe, Canada, and the northern United States.
Research into the causes of MS is ongoing. While we don’t know the exact trigger, most experts believe there is not one single cause – rather, it is the result of complex interactions between genes and environmental factors.
The role of genetics
MS is not directly inherited, but genetics do appear to play a role. Here are some key points about the genetic component of MS:
- Risk increases if a close family member has MS. For example, if one identical twin has MS, the other twin has a 25-30% lifetime risk of developing it too.
- Certain genes have been associated with higher MS risk, especially genes related to immune function.
- People whose ancestry traces to Northern Europe are at highest risk of MS, suggesting a potential genetic component.
- However, most people with MS-associated genetic markers do not develop the disease, indicating that genes alone cannot explain MS.
The role of environmental factors
Since genes cannot fully explain MS risk, scientists have researched various environmental factors that may trigger the disease in genetically susceptible individuals. Some proposed triggers include:
- Viral infections: Many viruses have been studied, including Epstein-Barr virus, human herpesvirus 6, and others.
- Vitamin D deficiency: Lower vitamin D levels are associated with higher MS risk.
- Smoking: Smoking significantly increases the risk of developing MS.
- Toxins or allergens: Some industrial chemicals and air pollutants have been suggested as possible MS triggers, but none proven.
- Geography: Areas farther from the equator have higher MS rates, possibly related to vitamin D levels.
While no definitive environmental trigger has been identified, viral infections and vitamin D deficiency during childhood are considered the most likely candidates based on existing research.
Is MS caused by a parasite?
Some researchers have speculated that MS could be caused by a parasite, but there is currently no strong evidence to support this theory. Here is an overview of the scientific research related to parasites as a potential cause of MS:
Chlamydia pneumoniae
Chlamydia pneumoniae is a common bacterial respiratory pathogen. Some early studies found evidence of C. pneumoniae infection in the cerebrospinal fluid of MS patients, leading to theories about its possible causal role.
However, subsequent larger studies failed to find an association between C. pneumoniae infection and MS. Most experts now agree that C. pneumoniae is highly unlikely to play a direct causal role.
Helicobacter pylori
Helicobacter pylori is a gastrointestinal bacterium that causes stomach ulcers. A few studies have found higher rates of H. pylori infection among MS patients than healthy controls.
However, later studies have not found evidence that H. pylori infection is related to MS risk or disease activity. More research is needed, but most evidence indicates it is unlikely that H. pylori causes MS.
Parasitic worms
Parasitic worm infections are uncommon in Western countries, but more common in developing regions of the world. Some researchers have hypothesized that lack of exposure to parasitic worms during childhood could influence immune system development in a way that increases MS risk later in life.
So far, studies have found no significant association between parasitic worm infections and MS risk. Clinical trials testing the therapeutic effects of intentional parasitic worm infection in MS patients are ongoing.
Toxoplasma gondii
Toxoplasma gondii is a common parasite that can infect humans via undercooked meat or contact with cat feces. Some research has found that people with MS have a higher rate of T. gondii antibodies compared to healthy controls.
However, most experts believe this association is unlikely to be directly causal. Instead, having MS may increase susceptibility to acquiring a Toxoplasma infection due to the weakened immune system.
Summary of the evidence
In summary, while associations between MS and certain bacteria or parasites have been occasionally reported, there is currently no strong evidence that MS is directly caused by a parasitic infection. Some key points:
- No parasite has been consistently detected in MS patients.
- Antibiotic or anti-parasitic drug trials have not improved MS symptoms.
- Regions with higher parasite exposure do not have lower MS prevalence.
- Parasites are unlikely to explain the geography and family history patterns of MS.
While the hygiene hypothesis is interesting, more high-quality research is needed to determine if eradicating parasites through modern public health initiatives has any relevance to MS risk.
What does cause MS?
While the exact cause remains unknown, experts believe the most likely explanation is a combination of genetic susceptibility plus one or more environmental triggers, possibly including a virus, vitamin D deficiency, or smoking. The immune system also clearly plays a central role in the pathology of MS.
Genetic susceptibility
MS is not directly inherited, but having a close family member with MS significantly increases your risk. Certain genes, especially those involved in immune function, may make people more susceptible to developing MS.
Possible environmental triggers
Proposed environmental triggers for MS include childhood viral infections, low vitamin D levels, and smoking. Geography and climate may also influence MS risk, possibly through sunlight exposure and vitamin D levels.
Immune system dysfunction
MS is widely considered to be an autoimmune disease, in which the body’s own immune system mistakenly attacks the myelin sheath surrounding nerve fibers. Both genetics and environmental triggers likely interact to lead to immune dysregulation.
Other possible factors
A few other factors associated with increased MS risk include obesity early in life, low omega-3 intake, and lack of sunlight exposure. Stress has not been shown to cause MS, but severe stress may worsen symptoms in established MS.
Treatments for MS
While there is no cure for MS, there are several therapeutic options that can modify the disease course, treat symptoms, and improve quality of life. The main categories of MS treatments include:
Disease-modifying therapies (DMTs)
DMTs help slow the progression of MS and reduce the frequency and severity of relapses. There are about 19 FDA-approved DMTs for MS, including:
- Interferon beta-based drugs like Avonex, Rebif, Plegridy, and Betaseron
- Glatiramer acetate drugs like Copaxone and Glatopa
- Monoclonal antibodies like Ocrevus, Lemtrada, and Tysabri
- Spingosine-1 receptor modulators like Gilenya
- Immunosuppressants like Mavenclad and Mayzent
Treating acute attacks
Acute MS relapses are often treated with short courses of corticosteroids to reduce inflammation and shorten attack duration.
Managing symptoms
A variety of medications help manage MS symptoms such as fatigue, pain, muscle stiffness, bladder problems, and more. Physical therapy, assistive equipment, occupational therapy, and other services also help.
Lifestyle measures for MS
In addition to medical treatment, certain lifestyle measures may help people with MS manage symptoms and improve quality of life. These include:
Diet
Eating a balanced, nutritious diet helps maintain energy levels. Some diets, like low saturated fat, may relieve fatigue and cognitive issues.
Exercise
Exercise improves strength, mobility, mood, bowel/bladder function, and cognition. Both aerobic and strength training are beneficial.
Stress management
Techniques like meditation, yoga, tai chi, and deep breathing can help control stress levels.
Supplements
Vitamin D, omega-3 fatty acids, and medical cannabis may potentially have benefits for MS patients.
Avoiding risk factors
Quitting smoking and avoiding obesity, especially in early life, may help limit MS progression.
MS prevalence rates
MS affects about 2.8 million people globally as of 2020. Here are details on MS prevalence in different world regions:
| Region | Prevalence |
|---|---|
| North America | 140 per 100,000 |
| Europe | 108 per 100,000 |
| Eastern Mediterranean | 14.9 per 100,000 |
| Southeast Asia | 2.8 per 100,000 |
| Africa | 2.1 per 100,000 |
| Western Pacific | 5 per 100,000 |
MS rates tend to increase with distance from the equator. Canada, northern US, New Zealand, southeast Australia and Europe have the highest prevalence globally.
MS diagnosis
There is no single test that can definitively diagnose MS. Instead, physicians use several factors:
Medical history
Detailed questions about symptoms and when they began. Family history is also considered.
Neurological exam
Assesses balance, coordination, vision, muscle strength and tone, reflexes, speech, and sensation.
MRI
Magnetic resonance imaging can detect MS lesions in the central nervous system.
Spinal fluid analysis
Cerebrospinal fluid is tested for antibodies, proteins, and signs of inflammation.
Evoked potential tests
Measures electrical signals in the central nervous system in response to stimuli.
A definite MS diagnosis requires evidence of damage in distinct areas of the CNS that occurred at different times, as seen on the tests above.
MS symptoms
Symptoms of MS vary significantly between patients and over the disease course. Common symptoms include:
Fatigue
About 80% of patients experience debilitating fatigue and low energy.
Mobility problems
Muscle weakness, spasms, balance issues, or vertigo can impair walking and coordination.
Pain
Chronic neuropathic pain or painful spasms affect many MS patients.
Vision issues
Optic neuritis, blurry vision, diplopia (double vision), and vision loss may occur.
Bladder/bowel problems
Overactive bladder, urinary frequency, incontinence, and constipation are common.
Cognitive changes
Issues with memory, attention, information processing, and executive functions.
Sexual dysfunction
Erectile dysfunction, reduced libido, and altered genital sensation affect both sexes.
Numbness
Tingling, numbness, or reduced sensation are common in the extremities or face.
Rarer symptoms include hearing loss, slurred speech, tremors, mood swings, and more. Symptoms often fluctuate day-to-day or over time.
MS prognosis and life expectancy
The prognosis for MS is highly variable depending on the disease course. Main prognostic factors are:
Age of onset
Earlier onset is linked to slower progression. Diagnosed after age 35 predicts faster progression.
Sex
Women tend to have more relapses but better recovery than men.
Type of MS
Relapsing-remitting MS has the best prognosis. Primary or secondary progressive MS have poorer outcomes.
Frequency of relapses
High relapse rates predict faster disability progression.
Response to treatment
Good response to disease-modifying therapies is linked to slower progression and less disability.
With treatment, average life expectancy is 5-10 years lower than the general population. MS is rarely directly fatal – most eventually die of other age-related diseases.
Types of multiple sclerosis
There are several clinical courses MS can take:
Clinically isolated syndrome (CIS)
First episode of MS symptoms, but does not yet meet criteria for definite MS diagnosis.
Relapsing-remitting (RRMS)
Distinct attacks followed by partial or full recovery; about 85% of patients start with this form.
Secondary progressive (SPMS)
Steady progression after initial relapsing-remitting course; occurs in 65% within 25 years.
Primary progressive (PPMS)
Steady worsening from onset with no distinct attacks; affects 10-15% at onset.
Progressive relapsing
Steady progression with occasional attacks on top; very rare.
Most transition between different clinical subtypes over the long-term disease course. RRMS often becomes SPMS later on.