What is stiff-person syndrome?

A rare neurological disorder that affects about one or two people per million is in the spotlight in the wake of an emotional social media post by pop star Céline Dion, who described her challenges with stiff-person syndrome.

Dion, 54, says she's been forced to cancel shows after years of struggling with muscle spasms and other health problems related to the debilitating neurological condition.

Because of its rarity, very few experts can speak knowledgeably on the disorder.

Johns Hopkins Medicine, a facility in Baltimore, Md., has a Stiff Person Treatment Center. In a video explainer on the facility's website, Dr. Scott Newsome, a neurologist at Johns Hopkins Medicine, says the syndrome is a very rare but "devastating" autoimmune disease. There's no clear cause, and the disorder is still being researched.

In the video, Newsome says the progressive condition shows up initially as a painful rigidity in muscles, causing spasms and imbalance. Newsome says the syndrome often causes a rigidity in the torso, lower back, abdominal and leg areas, affecting gait and balance.

"Just walking down the street, they could have a spasm and fall," Newsome explains.

Sufferers are sensitive — anxiety and even loud noises can lead to an excruciating spasm, according to Dr. Marinos Dalakas, professor of neurology and director of the neuromuscular division at Thomas Jefferson University School of Medicine in Philadelphia.

He says sufferers may walk like the "tin man" in The Wizard of Oz as their muscles spasm and contract.

"It is not pleasant. They walk like a statue," Dalakas told CBC in an interview.

He lauds Dion for speaking out about her personal struggle with the syndrome.

"It's very important because the syndrome will become more known ... and so the more people understand, the more physicians know about the syndrome, the earlier the diagnosis is made, the better treatment and more treatment will happen," said Dalakas.

In a post on the National Library of Medicine website, Texas neurologist Alexandra Muranova says the condition "has an insidious onset with gradual worsening over time and, if left untreated, can lead to permanent disability and mortality."

Newsome said that on average, it can take about seven years to reach a diagnosis. He says there is some evidence that the syndrome is related to an imbalance of gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter in the central nervous system.

GABA regulates the nervous system, so if its levels are low, he says that can create "spasticity" or hyper-excitability in the nervous system that looks like spasms, rigidness and tightness that leads to the disability.