Sheryl Ubelacker, The Canadian Press Published Tuesday, August 26, 2014 6:45AM EDT

TORONTO -- Canadian doctors have begun using stem cell transplants to treat "stiff person syndrome," a rare neurological condition in which a patient's leg and other muscles suddenly contract painfully, often leaving them immobilized like a tin soldier.

The disorder, which affects an estimated one in a million people, occurs when the immune system turns against a person's own tissues, in this case attacking cells in the brain and spinal cord.

Stem cell transplants have been used to treat patients with other auto-immune diseases, among them multiple sclerosis, scleroderma and Crohn's disease, but this may be the first time the procedure has been employed to alleviate the symptoms of stiff person syndrome, or SPS, the researchers reported Monday in the journal JAMA Neurology.

SPS is characterized by episodes of stiffness in the muscles and painful muscle spasms, which can be brought on by stress, loud noises or emotional distress. Some people with the disorder are so disabled they are unable to walk or move and may isolate themselves at home to avoid triggering an attack.

"Sometimes this happens when they're startled," said Dr. Harry Atkins of the Blood and Marrow Transplant Program at the Ottawa Hospital, who headed a team that transplanted stem cells into two women with the disease.

"So you can imagine walking across the street and someone honks the horn and you can't move, or you start falling and because your muscles can't move, you just fall and you hurt yourself," Atkins said Monday from Ottawa.

"It really does provide a barrier with just going on with your life."

Tina Ceroni of Toronto is one of the two SPS patients who had the stem-cell transplant -- and she said it has given back her life.

The personal fitness trainer, now 36, started getting severe symptoms in her late 20s. Initially she was diagnosed with hyponatremia, or low blood sodium, thought to be related to her heavy training schedule for a half-ironman competition.

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Canadian doctors use stem cells to treat 'stiff person syndrome'