Jan. 27, 2012 -- Environmental activist Erin Brockovich has launched her own investigation into the mysterious illness causing facial tics and verbal outbursts among 15 teenagers in Le Roy, N.Y.

Most of the teens have been diagnosed with conversion disorder -- a psychological condition that causes physical symptoms like jerky tics, convulsions and even paralysis. But Brockovich suspects groundwater contamination from a chemical spill from more than 40 years ago may be behind the Tourette-like symptoms.

"They have not ruled everything out yet," Brockovich told USA Today. "The community asked us to help, and this is what we do."

Don Miller, whose 16-year-old daughter, Katie, still suffers from debilitating tics, said his sister contacted Brockovich for help.

"We're just trying to eliminate everything, and she wants to eliminate that it's the environment," said Miller. "It's a possibility and she wants to either prove it is or it isn't something in the environment."

Brockovich, who famously linked a cluster of cancer cases in California to contaminated drinking water prompting an Oscar-winning movie starring Julia Roberts, said a derailed train spilled cyanide and trichloroethene within about three miles of Le Roy High School in 1970. All 15 of the affected teenagers -- 14 girls and one boy -- attended the school when they started showing symptoms last fall.

"When I read reports like this that the New York Department of Health and state agencies were well-aware of the spill and you don't do water testing or vapor extraction tests, you don't have an all-clear," Brockovich told USA Today.

An investigation by the New York Department of Health found "no evidence of environmental or infection as the cause of the girls' illness," according to department spokesman Jeffrey Hammond. "The school is served by a public water system. ... An environmental exposure would affect many people."

Doctors also ruled out Pandas -- a neurological disorder linked to streptococcal infections -- and the Gardasil HPV vaccine, which many of the girls did not receive, Hammond said.

The school was tested for volatile organic compounds by an independent company. But "people are free to pursue additional environmental testing," Hammond said.

Twelve of the teens -- all of them girls -- have been diagnosed with conversion disorder in which the emotional response to a stressful situation can manifest itself as physical symptoms. Three new suspected cases are still being examined. Women are more likely to get conversion disorder than men, and teens are at a higher risk than adults. But some parents want a second opinion.

"We don't really agree with it," Miller said of the diagnosis. "Down the road, who knows. But for them to give that diagnosis, they have to rule everything else out. And they haven't done that."

The National Institutes of Health has offered to help solve the puzzle. Dr. Mark Hallett, chief of the NIH Medical Neurology Branch, said the cluster of cases offers a unique research opportunity.

"We have offered our help but have not been asked for yet," said Hallett, adding that he has not yet seen any of the teens. "One of the difficulties in this is that there hasn't been a lot of attention to this problem or very much research into it, which has made it somewhat of a mysterious disorder."

Hallett said conversion disorder is common, affecting as many as two people at his movement disorders clinic each week. But he said it's rare to see a large group of people with the same symptoms.

"We don't understand that aspect of it completely," Hallett said of the potential for conversion disorder to spread through a group, a characteristic that once earned it the name "mass hysteria." "For some reason, the brain mimics things that they know. ... It's just one of the ways the brain reacts to psychological stress. We don't understand why, but it truly is involuntary just as patients say it is."

Lydia Parker, a senior at Le Roy High School, has symptoms so severe she spends most of the day in a wheelchair.

"I can't stand for more than about two minutes," said 17-year-old Parker. "And my vocal and tic and everything gets really bad at night."

Parker said she's glad Brockovich is drawing attention to the disorder, but she doesn't think the answer is in the school's water supply.

"I didn't eat the food, I didn't drink the water. … I brought my own Snapples," she said. "I don't even borrow pencils."

Parker said her younger brother goes to the same school and has no symptoms. "If it was something in the environment, it would have kicked in and a lot more people would have gotten it," she said. But she doesn't think it's stress is the answer, either.

"Conversion disorders are brought on by stress, she said. "Just being a senior isn't that stressful; you just have fun."

Hallett said he's not surprised the teens and their families were looking for another, nonpsychological explanation.

"It always seems to be the case that patients far prefer to have a [medical] diagnosis than a psychological one," he said.

The possibility of an environmental trigger has been bolstered by reports of similar symptoms in two teens living in Corinth, a town 250 miles from Le Roy. The girls started showing symptoms in May, around the same time they passed through Le Roy on their way to a softball tournament in Ohio.

"We have two girls out here that were showing these symptoms before those girls," said Randall Nicholson, whose daughter Alycia continues to have tics and even seizures. "Is it just a coincidence? Is this the same as what they have or are we dealing with two completely different animals here?"

Nicholson said it's been hard for his daughter, who just turned 16.

"She's so excited about getting to drive. How do you tell her, 'No, you can't."

If it is conversion disorder, there are treatments. Psychotherapy and stress management can improve the symptoms, which usually subside within a few weeks.

Miller said his daughter Katie has good days and bad days.

"On Wednesday I brought her to cheerleading practice and she was fine. But when she got home, she had verbal tics for almost an hour -- just loud verbal tics," he said. Katie is still attending school but spends half her time at home sleeping, exhausted from her uncontrollable symptoms, Miller said. "Yesterday she seemed better, but who knows today."