Dion announced Thursday that she had postponed dates for her European tour next year due to the condition.
"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," the singer said in an Instagram video.
People with stiff-person syndrome often experience rigidity in their torso and limbs, as well as severe muscle spasms that can cause them to fall down. The spasms can occur at random or be triggered by certain stimuli, including loud noises, touch and emotional distress.
Dr. Richard Nowak, an assistant neurology professor at the Yale School of Medicine, said the condition "has a range of severity, from quite mild — easily managed with a little bit of medication — to folks that are quite severe that can be, frankly, quite disabled from it."
Stiff-person syndrome overall disrupts the normal pathways of communication between the brain and the muscles.
"There’s a massive firing that’s occurring from the central nervous system, down through the spinal cord, down through the nerves as they plug into the muscles, and it’s causing them to become rigid or go into spasm, which equals the stiffness," Nowak said.
In most but not all cases, people with stiff-person syndrome have elevated levels of antibodies that target a particular protein involved in the process of controlling muscle function. Doctors consider these patients to have an autoimmune condition.
"In stiff persons, the pathways that are attacked are the brake pathways, so you’ve lost your brakes on your muscles," said Dr. Simon Helfgott, a rheumatologist at Harvard Medical School. "Once your muscle starts to contract, it doesn’t have a way to stop itself from contracting."
Helfgott estimated that about two-thirds of stiff-person patients have these antibodies, which can be picked up by a blood test. But around 30% don’t, he said, so researchers don’t fully understand what’s driving their illness.
A small minority of cancer patients may also produce antibodies that attack the nervous system and trigger stiff-person syndrome, Helfgott added.
Symptoms of the syndrome go beyond the normal muscle cramps that most people experience from time to time, Helfgott said; instead, the muscles tend to lock up. Some of his patients have had difficulty walking or required wheelchairs, he added.
"This is just such a severe diagnosis to have, especially if you’re an entertainer [on] the world-class type of stage," Helfgott said. "It’s going to be very, very challenging to be able to continue."
Because many symptoms of stiff-person syndrome overlap with those of Parkinson’s disease, multiple sclerosis, fibromyalgia or anxiety, it often takes time to diagnose. Doctors rely on several tools to do that, including MRIs of the brain or spinal cord, blood tests or electromyography tests that use tiny needles to measure a person's muscle and nerve responses.
Helfgott said the syndrome is harder to treat than other autoimmune disorders like rheumatoid arthritis or Crohn’s disease, and there is no cure.
Muscle relaxants or Botox injections can help relieve milder symptoms like spasms, Nowak said. Patients with more severe symptoms are often prescribed intravenous immunoglobulin, an infusion that has been shown to reduce people's stiffness and sensitivity to noise, touch and stress.
But the symptoms and their severity levels can vary minute by minute, Helfgott said, and it's difficult to predict whether a patient's condition will get worse over time.
"In some cases, the condition can level off and stay the way it is. I have people who are like that — they're no different now than they were 10 years ago," he said. "In others, it is a slow, subtle decline."