Canadian superstar Céline Dion cancelled her "Courage" world tour, citing ongoing health problems due to a rare neurological disorder called "stiff person syndrome." Dion performs Wednesday, Sept. 18, 2019 at the Videotron Centre in Quebec City. THE CANADIAN PRESS/Jacques Boissinot

Canadian superstar Céline Dion cancelledthe rest of her "Courage" world tour Friday, citing ongoing health problems due to a rare neurological disorder called "stiff person syndrome."

Dion's team did not reveal specific symptoms the 55-year-old singer was experiencing, but said the songstress was "unable to successfully prepare for and perform the remainder of the tour."

According to the Stiff Person Syndrome Center at Johns Hopkins Medicine, the incurable condition causes muscle stiffness and painful spasms that worsen over time, which can be triggered by sudden movement and unexpected loud noises.

The name doesn't do justice to the pain and life-changing symptoms the syndrome causes, said Tara Zier, founder of the Stiff Person Syndrome Research Foundationin Bethesda, Md.

"A lot of people have challenges with mobility. Many have assisted devices for mobility, walkers, wheelchairs. Some people are bedridden,'' she said.

Here's a look at stiff person syndrome:

HOW COMMON IS IT?

It's generally reported that about one or two people per million are affected but researchers don't know for sure, said Dr. Marinos Dalakas, director of the neuromuscular division at the Thomas Jefferson School of Medicine in Philadelphia.

The number of cases could be higher because it's often misdiagnosed as Parkinson's disease, multiple sclerosis or psychiatric disorders, said Dalakas, who is also a member of the medical advisory board for The Stiff Person Syndrome Research Foundation.

WHAT ARE THE SYMPTOMS?

Muscle rigidity and spasms are the two main defining symptoms, which can be very painful and can cause people to fall, Dalakas said. Older people, especially, can become physically disabled. If the thoracic muscles are affected, people can have difficulty breathing and their voice may tremble.

If the muscle stiffness is severe, "you can become like a statue,'' he said.

Fear of spasms also causes anxiety and may make some peopleafraidto leavetheir homes.

IS THERE A CURE?

No. But there are treatments that can help alleviate symptoms.

Medications mustbe tailored to each patient andtheir symptoms, Dalakas said.

Common prescriptions include diazepam, which can help relieve muscle spasms and reduce severe anxiety, as well as muscle relaxants and anti-seizure medications like gabapentin.

HOW IS IT DIAGNOSED?

A blood test is used to detect the presence of antibodies against an enzyme called glutamic acid decarboxylase (GAD). Doctors may also physically examine the person's muscles or use electromyography (EMG) to assess muscle and neurological function.

WHAT CAUSES IT?

Like with many autoimmune diseases, the cause is not known, Dalakas said.

But there's reason for patients to be hopeful, he said, becausesymptoms can often be controlled. The earlier patients are diagnosed and treated, the better their outcomes tend to be.

This report by The Canadian Press was first published Dec. 8, 2022 and was updated May 26, 2023.

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