Celine Dion's new documentary "I Am: Celine Dion," released June 25, gives fans and viewers an inside look at the iconic singer's battle with stiff-person syndrome.
Back in December 2022, Dion announced publicly in that she had been diagnosed with the neurological disease, shining a spotlight on the rare condition.
In a taped video message shared to her Facebook and Instagram pages at the time, the legendary performer, 56, said, "I have been diagnosed with a very rare neurological disorder called the stiff-person syndrome, which affects something like 1 in 1 million people."
Dr. Leah Croll, an assistant professor of neurology at the Lewis Katz School of Medicine at Temple University in Philadelphia, sees and treats patients with neurologic diseases that affect the brain, spinal cord or peripheral nerves, including stiff-person syndrome.
Croll agreed with Dion's statement that stiff-person syndrome is not common, calling it an "exceptionally rare disease."
"It occurs only in about one to two people per million," Croll previously told "Good Morning America."
Croll explained that people between the ages of 20 and 50 tend to be diagnosed with stiff-person syndrome, and although rare, it can appear in children and older adults too.
Overall, women are "two to three times" more likely to have stiff-person syndrome than men.
"We think it's because this disease may have an autoimmune component, and in general, women are [at] higher risk for autoimmune diseases," Croll said. "But this is theoretical. We're not totally certain as of yet."
In her video, Dion revealed some of the symptoms of stiff-person syndrome she has experienced.
"While we are still learning about this rare condition, we now know this is what has been causing all of the spasms I have 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 chords to sing the way I am used to," she said.
Croll said other symptoms that can indicate someone has stiff-person syndrome include rigidity and stiffness of certain areas of the body causing unsteadiness, slower movements and difficulties walking, something Dion said she has had in addition to difficulties singing.
"Typically, patients will present with stiffness in the muscles of the trunk, neck and back, and also … the shoulders and the hips. In some cases, patients may have the disease that only implicates maybe just one limb, so like just one leg is affected," Croll said.
"The key here is that this stiffness would be so profound that it impairs someone's ability to move normally," Croll added. "And the most common symptom for these patients is going to be difficulties with walking."
Croll also noted that people with stiff-person syndrome symptoms can also develop other conditions, like anxiety and phobias, as a result of their physical symptoms.
MORE: New Celine Dion doc will detail experience with stiff-person syndrome: 'I wanted to document this part of my life'There are treatments available to address the symptoms of stiff-person syndrome but there is currently no cure for the chronic and progressive condition.
"Most patients, as a first line, will be given medications that are meant to help relax the muscles. And in some patients, their doctors may also choose to pursue certain therapies that are meant to modulate the immune system," Croll said. "It's important though to point out that these are therapies that are meant to lessen the severity of symptoms or potentially slow the progression of symptoms, but we don't have a therapy available that specifically targets this disease."
As stiff-person syndrome is rare, there has not been sufficient research and Croll said there are currently no major clinical trials for the disease.
Doctors do not currently know whether stiff-person syndrome impacts an individual's life expectancy, according to Croll, who said some patients have lived a few years after diagnosis while others have gone on to live for decades.
Croll cautioned that stiff-person syndrome is not commonly seen in the general population but advised that individuals concerned about symptoms they're experiencing can start a discussion with their primary care provider who can also provide a referral to a neurologist.
"This is a very rare condition that most people should not worry about. But anyone who is experiencing symptoms in their muscles that are interfering with their ability to move normally would benefit from consultation with a neurologist to work that up," Croll said.