Multiple sclerosis (MS) is the most widespread disabling neurological condition of young adults around the world. You can develop MS at any age, but most people receive diagnoses between the ages of 20 and 50.

There are relapsing, remitting, and progressive types of MS, but the course is rarely predictable. Researchers still don’t fully understand the cause of MS or why the rate of progression is so difficult to determine.

The good news is that many people living with MS don’t develop severe disabilities. Most have a normal or near-normal lifespan.

There’s no national or global registry for new MS cases. Known figures are only estimates.

Recent findings from a National MS Society study estimate nearly 1 million people in the United States are living with MS. This is more than double the last reported number, and the first national research on MS prevalence since 1975. The society also estimates that 2.3 million people live with MS globally. About 200 new cases are diagnosed each week in the United States, says the MS Discovery Forum.

Rates of MS are higher further from the equator. It’s estimated that in southern U.S. states (below the 37th parallel), the rate of MS is between 57 and 78 cases per 100,000 people. The rate is twice as high in northern states (above the 37th parallel), at about 110 to 140 cases per 100,000.

The incidence of MS is also higher in colder climates. People of Northern European descent have the highest risk of developing MS, no matter where they live. Meanwhile, the lowest risk appears to be among Native Americans, Africans, and Asians. A 2013 study found only 4 to 5 percent of all diagnosed MS cases are in children.

Far more women have MS. In fact, the National MS Society estimates MS is two to three times more common in women than men.

MS is not considered an inherited disorder, but researchers believe there may be a genetic predisposition to developing the disease. About 15 percent of people with MS have one or more family members or relatives who also have MS, notes the National Institute of Neurological Disorders and Stroke. In the case of identical twins, there’s a 1 in 3 chance for each sibling to have the disease.

Researchers and neurologists still can’t say with certainty what causes MS. The ultimate cause of MS is damage to myelin, nerve fibers, and neurons in the brain and spinal cord. Together these make up the central nervous system. Researchers speculate that a combination of genetic and environmental factors is at play, but it’s not fully understood how.

The relationship of the immune system and the brain, however, could be considered a culprit. Researchers suggest the immune system could mistake normal brain cells for foreign ones.

One thing the MS community knows for certain is that the disease is not contagious.

Clinically isolated syndrome (CIS)

CISis considered to be one course of MS, but it may or may not progress to MS.To get a diagnosis of MS:

  • A
    person has to experience a neurologic episode (typically lasting 24 hours or
    more) that resulted in damage to the central nervous system.
  • It’s
    likely this episode will develop into MS.

People who are at high risk of developing MS are found to have MRI-detected brain lesions. There’s a 60 to 80 percent chance of receiving an MS diagnosis within a few years, estimates the National MS Society. Meanwhile, people at low riskdon’t have MRI-detected brain lesions. They have a 20 percent chance of receiving an MS diagnosis in the same amount of time.

Relapsing-remitting MS (RRMS)

RRMS is characterized by clearly defined relapses of increased disease activity and worsening symptoms. These are followed by remissions when the disease doesn’t progress. Symptoms may improve or disappear during remission. Approximately 85 percent of people receive a diagnosis of RRMS at first, says the National MS Society.

Secondary progressive MS (SPMS)

SPMS follows an initial RRMS diagnosis. It sees disability gradually increase as the disease progresses, with or without evidence of relapse or changes in an MRI scan. Occasional relapses may occur, as will periods of stability.

Untreated, about 50 percent of people with RRMS transition to SPMS within a decade of the initial diagnosis, estimates a 2017 study. About 90 percent of people transition within 25 years.

Primary progressive MS (PPMS)

PPMS is diagnosed in about 15 percent of people with MS, estimates the National MS Society. People with PPMS experience a steady progression of the disease with no clear relapses or remissions. The rate of PPMS is equally divided between men and women. Symptoms usually begin between the ages of 35 and 39.

A high percentage of MS cases don’t progress. These may fit into a subgroup with a “very stable benign” form of the disease, per a 30-year study presented in 2017. Researchers say it’s possible for people to remain in the RRMS phase for 30 years.

At the other end of the spectrum, a 2015 study found about 8 percent of people with MS develop a more aggressive course of the disease. It’s known as highly active relapsing-remitting multiple sclerosis (HARRMS).

Symptoms vary a great deal from one person to another. No two people have the same combination of symptoms. This, of course, complicates identification and diagnosis.

In a 2017 report, one-fifth of European women surveyed received misdiagnoses before eventually receiving an MS diagnosis. The average woman was found to go through about five visits with a healthcare provider over the course of six months before reaching a diagnosis.

According to the MS Foundation, symptoms can impact the mind, body, and senses in a number of ways. These include:

  • blurred or double
    vision, or total vision loss
  • hearing impairment
  • reduced sense of taste
    and smell
  • numbness, tingling, or
    burning in limbs
  • loss of short-term
  • depression, personality
  • headaches
  • changes in speech
  • facial pain
  • Bell’s
  • muscle spasms
  • difficulty swallowing
  • dizziness, loss of
    balance, vertigo
  • incontinence,
  • weakness, fatigue
  • tremors, seizures
  • erectile dysfunction,
    lack of sexual desire

There’s no single “MS test.” To receive a diagnosis, your doctor needs to collect your medical history and perform a neurological examination and a series of other tests. Tests may include:

  • MRI
  • spinal fluid analysis
  • blood tests
  • evoked potentials (such as an EEG)

Since the exact cause of MS is still unknown, there’s no known prevention.

There’s also no cure for MS yet, but treatments can manage symptoms. MS medications are designed to lessen the frequency of relapses and slow the progression of the disease.

There several disease-modifying medications approved by the U.S. Food and Drug Administration to treat MS. They include:

  • teriflunomide (Aubagio)
  • interferon beta-1a
    (Avonex, Rebif, Plegridy)
  • interferon beta-1b
    (Betaseron, Extavia)
  • glatiramer acetate
  • fingolimod (Gilenya)
  • mitoxantrone
  • dimethyl fumarate
  • natalizumab (Tysabri)
  • ocrelizumab
  • alemtuzumab (Lemtrada)

People with MS can safely carry a baby to term. Pregnancy doesn’t generally affect MS in the long term.

MS has been found to affect decisions about pregnancy, though. In a 2017 survey, 36 percent of women participants decided not to have children at all or postponed the timing of getting pregnant due to their MS.

While people with MS often experience a relief from symptoms during pregnancy, about 20 to 40 percent have a relapse within six months of giving birth.

MS is an expensive disease to treat. A 2016 economic analysis of MS found the total lifetime costs per person with MS to be $4.1 million. The average yearly healthcare costs range from $30,000 to $100,000 based on the mildness or severity of the disease.