(CNN) When 7-year-old Bailey Sheehan arrived at a hospital in Oregon partially paralyzed, a doctor said the girl was faking her symptoms to get her parents' attention because she was jealous of her new baby sister.
But that doctor was proved wrong when an MRI showed that the girl had acute flaccid myelitis or AFM, a polio-like disease that's struck hundreds of children since 2014.
Erin Olivera, mother of a child with AFM and founder of a private Facebook page for parents of 400 children with the disease, says Bailey's experience is hardly unique. She estimates that based on postings by parents, as many as 1 in 10 children were told that the paralysis was all in their heads when they first sought medical care.
Experts who study the art and science of diagnosis say the problem goes beyond this one rare disease. They say that in general, when presented with a puzzling disease, physicians too often leap to a diagnosis of a psychiatric problem.
"Mental disorders become the default position to deal with medical uncertainty," said Dr. Allen Frances, former chair of psychiatry at the Duke University School of Medicine. "It's widespread, and it's dangerous."
Dr. Mark Graber, president emeritus of the Society to Improve Diagnosis in Medicine, added, "It's a tendency that physicians have when they can't find a physical cause.
"It's bad. It's very bad."
Bailey was a healthy little girl until October 28, 2014, when she suddenly couldn't move her neck or her right shoulder or leg.
A rehabilitation expert at a children's hospital said Bailey wasn't really paralyzed, according to her mother, Mikell Sheehan.
The doctor said the paralysis was an emotional reaction to her sister's birth four months earlier. He diagnosed Bailey with a mental condition called conversion disorder.
Sheehan told the doctor off.
"I said, 'You've been with my child for 15 minutes, and you think it's psychological? Get out of my face,' " she remembered.
Sheehan said the doctor hinted that she was unstable.
"He said, you know, 'moms with new babies don't get enough sleep,' " she said.
Bailey's regular pediatrician, who'd known the girl since birth, disagreed with the diagnosis and pushed for further testing. That's when the MRI showed that she had AFM.
Armed with the correct diagnosis, Bailey received treatment for AFM, including extensive physical therapy, and four years later is walking again.
"We were lucky that her pediatrician was such an advocate for us, but I don't know if everyone's that lucky," Sheehan said.
Sheehan says she understands why doctors didn't immediately think of AFM for her daughter, because the disease was not well-known four years ago. But there are several other causes of paralysis in children, and she wonders why her daughter didn't get a full round of testing for those.
Dr. Benjamin Greenberg, a neurologist who's seen cases of AFM across the country, said that even this year, when AFM has made headlines nationally, parents have told him that doctors have missed the disease and suggested that their children were faking their paralysis.
"The stories I can tell are maddening and saddening," said Greenberg, associate professor of neurology at UT Southwestern Medical Center.
Four years later, Sheehan says, she still feels the scars from her daughter's misdiagnosis.
"You feel violated and wrongly accused," she said.
Though there's no data indicating how frequently doctors misdiagnose physical conditions as psychiatric ones, experts in the field of diagnosis say they see it all too often.
It typically starts when a patient has a perplexing illness and doctors feel a need to come up with a diagnosis.
"Doctors are uncomfortable with not having answers," Frances said.
The consequences can be "catastrophic," he said, because a misdiagnosis can lead to a patient receiving treatment for a disease they don't have and missing out on treatment for the disease they do have.
"False certainty is much more dangerous than uncertainty," he said.
The American Medical Association and the American College of Emergency Physicians declined requests for comment.
Graber, who is also professor emeritus of medicine at the Stony Brook University in New York, said part of the problem is that medical students are taught that physical symptoms sometimes have a psychological basis. That's true, he said, but doctors need to thoroughly test for physical problems before defaulting to a psychiatric diagnosis.
"Physicians have an obligation to do a thorough workup before turning to a psychological explanation," he said. "When a doctor can't find a cause, that's a great time to get a second opinion or consult with a specialist."
Frances added that it's OK for a doctor to simply say "I don't know."
"Doctors need to learn to embrace medical uncertainty," he said.