Medical Mystery: One day, she couldn’t walk straight. Doctors were stumped.

"What are you doing?" Laura Hsiung's friends asked as she slowly loped across a Maryland handball court in 2010, her ankle off-kilter so that she was walking on the outside of her left foot.

Hsiung, who lives in Montgomery County, Md., recalls wondering the same thing. One minute she was walking normally, and then all of a sudden, she wasn't.

"I couldn't figure it out," Hsiung said. "I hadn't rolled my ankle. But my left foot just would not function normally."

All her life, Hsiung had been an athlete. Her skills as a gymnast had won her an athletic scholarship to the University of New Hampshire. She was also an avid runner and played competitive volleyball well into her 30s.

After the episode on the handball court, a Montgomery County podiatrist took X-rays of her ankle but found nothing amiss. The doctor diagnosed "generalized weakness" and referred Hsiung, then 46, to a physical therapist.

She saw the physical therapist regularly for six months. He tried taping her ankle in the hope that would regularize her gait. He also prescribed a regimen of stretching exercises and ordered custom-made orthotics for her shoes. None of these measures helped.

When she walked, Hsiung's left foot kept rolling outward, a movement called supination."My ankle ached, my toes were scrunched, and I had to think about every step because I was constantly trying to compensate," she recalled.

Her grandfather had suffered from Parkinson's disease and early in his illness had developed foot drop, which involves difficulty lifting the front of the foot.

Hsiung worried that her problem might be an early sign of Parkinson's, although she showed no other symptoms.

She knew she needed to have both knees replaced because of pain caused by significant wear and tear.

"I figured I should go ahead and do the knee replacements because they might help," she said.

In March 2011 Hsiung underwent a double knee replacement. Although the surgery greatly improved her knee function, her odd walk remained. "I thought, 'Oh, my gosh, this is not fixed.' "

She returned to the podiatrist. He proposed an operation to remove a ganglion cyst, a benign growth on her left ankle, which he thought might be impinging on a joint.

That surgery, performed in December 2011, didn't help, either.

Neither did a consultation the following month with an osteopath who specializes in gait disorders.

Her next stop was a neurologist. He ordered EMG testing, which assesses nerve function, along with MRI scans of Hsiung's back and ankle. All were normal.

In June 2012, she was referred to John Jowers, a physical therapist. After listening to Hsiung's account of her sudden problem, Jowers decided to videotape her walking on a treadmill in order to more precisely analyze her gait.

Muscle weakness clearly wasn't the cause. "Laura had great strength and coordination," he noted.

But Jowers spotted something else: When she took a step backward or sideways, her foot behaved normally.

"It was pretty clear that this wasn't orthopedic," Jowers said, in part because she seemed unable to control her foot by focusing on her movements. He suspected her problem might be neurological.

Jowers said he thought of an unusual condition he had learned about a few years earlier in a continuing medical education class. Called task-specific focal dystonia, the movement disorder can occur after repetitive use — or overuse — of certain muscles; the cause is unknown but is probably the result of genetic and environmental factors and may reflect dysfunction in the parts of the brain that govern movement.

In people with this disorder, involuntary muscle contractions or uncontrolled movements develop without warning. Writers can develop it (in which case it's called writer's cramp), as can people playing a musical instrument such as piano or guitar (musician's dystonia) and those engaged in sports, including running (where it's known as repetitive exercise dystonia, or runners' dystonia).

"You'll probably never see this," Jowers remembers the instructor telling the class, "but just in case, keep it in the back of your mind."

The disorder is rare, affecting an estimated seven to 69 people out of a million. Approximately 1 percent of musicians suffer from dystonia severe enough to impair their performance, among them virtuoso pianists Leon Fleischer and the late Glenn Gould.

A recent study of repetitive exercise dystonia found that it is often misdiagnosed as an orthopedic or even a psychological problem.

In November 2017, Justine Galloway, a 28-year-old with runner's dystonia, completed the New York City Marathon in just over six hours by running backward, which seems to allow her brain to fire properly.

The disorder is not curable. Treatments, which include Botox injections and levodopa, a drug used to treat Parkinson's disease, have been found to ease the problem.

During their second meeting, Jowers told Hsiung that he suspected the disorder might be causing her foot problem and suggested that she consult a neurologist.

A few months later, after Hsiung consulted a dystonia specialist in Manhattan, the diagnosis Jowers suspected was confirmed.

"It was a relief to finally have a name for this," Hsiung said, "but I couldn't fix it."

She began taking levodopa, which has helped normalize her walk. Hsiung also discovered that walking on uneven terrain, such as a hiking path, is much easier than walking in a mall.

Hsiung's two-year ordeal, and her intense frustration with the many doctors who showed little interest in resolving her problem, spurred her to make a life change.

In 2014, she left a 28-year career selling legal software and enrolled in a 2½-year program at Montgomery College, where she earned a degree as a physical therapy assistant.

Hsiung said she was drawn to the profession by the sports-related injuries she sustained over the years and by her experience with Jowers, whom she described as "the only one who was willing to take the time to figure out what was wrong."

For two years, Hsiung has worked at a clinic with wounded military personnel at the Walter Reed National Military Medical Center in Bethesda. "I think the experience has made me a better therapist," she said.