On Thursday, singer Céline Dion announced that she is suffering from stiff-person syndrome (SPS)—a rare neurological condition that has caused "severe and persistent muscle spasms," affecting "every aspect" of her life.

Céline Dion's rare diagnosis

In an Instagram video posted Thursday discussing her world tour, Dion revealed that she has been diagnosed with SPS.

"I wasn't ready to say anything before, but I'm ready now. I've been dealing with problems with my health for a long time, and it's been really difficult for me to face these challenges and to talk about everything that I've been going through," Dion said.

According to Dion, the rare neurological disorder has been causing her "severe and persistent muscle spasms," and has even affected her ability to walk and sing.

"While we're still learning about this rare condition, we now know this is what's been causing all of the spasms that I've been having. Unfortunately, these spasms affect every aspect of my daily life, sometimes causing difficulties when I walk and not allowing me to use my vocal cords to sing the way I'm used to," Dion said. 

"I have to admit it's been a struggle. All I know is singing, it's what I've done all my life," she added. "I always give 100% when I do my shows, but my condition is not allowing me to give you that right now."

Currently, Dion is focusing on her health. "I have a great team of doctors working alongside me to help me get better," Dion said. "I'm working hard with my sports medicine therapist every day to build back my strength and my ability to perform again."

What is stiff-person syndrome?

According to the National Institute of Neurological Disorders and Stroke (NINDS), SPS is a rare "neurological disorder with features of an autoimmune disease."

"It's a disease that's characterized by progressive muscle stiffness, muscle spasms, rigidity—typically in the muscles of the back, specifically the lower back, as well as the upper legs," said Kunal Desai, a Yale Medicine neurologist and assistant professor of neurology who specializes in neuromuscular disease.

Notably, the condition is very rare, affecting "only about one or two in a million people," according to Johns Hopkins Medicine (JHM).

While the underlying cause of SPS remains unknown, many experts believe it may be an autoimmune disorder that can occur with other autoimmune conditions.

The condition can be diagnosed through antibody testing. However, a study published last week in Neurology found that SPS is often misdiagnosed as a variety of non-neurological conditions. "Improved diagnostic accuracy will reduce exposure to unnecessary treatments and health care costs," the study authors wrote.

There is currently no cure for SPS. However, its symptoms can be managed through drugs that decrease muscle stiffness and spasms, stretching, massage, acupuncture, and other therapies, according to the National Organization for Rare Disorders.

Still, people with SPS are often hunched over with a stiff posture and may have a hard time walking or moving. Others may be "afraid to leave the house because street noises, such as the sound of a horn, can trigger spasms and falls," according to NINDS.

Since they often lack "normal defensive reflexes," people with SPS are prone to falls, and can get injured easily, NINDS said.

In addition, SPS triggers "progressive muscle stiffness and painful spasms," which can be set off by environmental factors like "sudden movement, cold temperature or unexpected loud noises," according to JHM.

With severe muscle spasms, "the muscles can feel tight as a rock. So, it can be very, very uncomfortable and painful," Desai said, noting that other stimuli that can sometimes trigger these spasms include contact with the muscles, "certain subtle movements," and stress. (Grantham-Phillips, USA Today, 12/9; Bendix, NBC News, 12/8; Martichoux, Nexstar Media Wire/The Hill, 12/8; Olson, NPR, 12/8; Tourne, ScienceAlert, 12/9)