Selma Blair revealed this week she was leaving “Dancing with the Stars” due to complications from multiple sclerosis. The disease, commonly referred to as MS, affects nearly 1 million adults in the U.S. and it could be disabling. 

Most people receive an MS diagnosis between the ages of 20 and 40 and the disease is more common in women than men, according to the Cleveland Clinic, a nonprofit academic medical center.

MS is a disease of the brain and spinal cord and it can disable people because it affects the central nervous system, according to Mayo Clinic, another nonprofit academic medical center. The myelin, or protective sheath that covers nerve fibers, is attacked by the immune system, resulting in communication problems between the brain and the rest of the body.

The cause of the disease is unknown, but people whose parents or siblings has had MS are at higher risk of developing the disease. Some viruses, including Epstein-Barr, the virus that causes infectious mononucleosis, have been linked to MS. White people are at the highest risk, as are people in countries with temperate climates, including Canada, the northern United States, New Zealand, southeastern Australia and Europe.

Symptoms can vary – but severe symptoms include the inability to walk. Others may experience numbness or weakness in their limbs, electric-shock sensations that occur with some neck movements, or tremors. MS can also affect vision and speech, cause dizziness and fatigue, and a number of other symptoms. 

Some people may have long periods of remission from MS and don’t experience new symptoms for quite some time.

Blair revealed she had MS in 2018 that she has multiple sclerosis, and has frequently appeared at public events using a cane to help her walk. 

The actress, who was a contestant on the current season of “Dancing with the Stars,” said recent MRI results led her to make the decision to leave the show. 

“There’s just intensive bone trauma and inflammation among rips and tears,” she said in a video announcing her departure. “So I could do extensive damage that, of course, I do not want. I’ll have to settle in and get back to being a mom and showing them I have to pull back on something that I love doing.”

She and her dancing partner, Sasha Farber, shared one last waltz on the show Monday night. 

She was emotional during an interview after her final dance on the show, but said the competition helped her improve physically.

“I’m so much better, and I would have never had the motivation to push myself in that way if it weren’t for this kind of thing with Sasha,” she said.

Many people with MS experience a recurrence of symptoms during the course of the disease. New symptoms can develop over weeks or days and can then improve partially or completely. Remissions can last months or even years, according to Mayo Clinic. 

The severity of symptoms can also worsen over time and often includes problems with mobility and gait.

Making a confirmed diagnosis of MS is not always easy since early symptoms may be minor and sporadic, according to Johns Hopkins Medicine. Other diseases can also have similar warning signs.

There is no definitive single laboratory test to confirm the diseases but multiple neurological exams, like an MRI, usually help physicians make a diagnosis. 

Caitlin O’Kane

Caitlin O’Kane is a digital content producer covering trending stories for CBS News and its good news brand, The Uplift.