It was supposed to be a typical ballet class. Cynthia Toussaint, then a senior dance major at the University of California, Irvine, engaged in her usual stretching routine: she raised her left leg to the barre and slowly bent her upper body down to her right knee.
For a moment, she delighted in the long stretch. But as she returned to an upright position, she felt a sudden pop in her hamstring. "It felt like a guitar string had been plucked and it had broken," said Ms. Toussaint, who is now 45.
An intense burning sensation followed; it felt as if her leg had been doused in gasoline and set on fire, she said. The next day, the college athletics trainer determined that she had pulled her hamstring. But even years later, the pain would not subside. It migrated to her other leg, leaving her bedridden for nearly a decade, and overtook her vocal cords, leaving her temporarily mute.
All the while, doctors puzzled over and even doubted her mysterious condition.
Ms. Toussaint now knows that she is among an estimated one million Americans living with complex regional pain syndrome, a nerve disorder formerly known as reflex sympathetic dystrophy syndrome. For patients with the disorder, a trauma as mild as a fractured wrist or a twisted ankle can cause the nerves to misfire, so much so that intense pain messages are constantly sent to the brain.