Photos by Josh Meltzer | The Roanoke Times

Angela Bradshaw, mother of two William Byrd High School students, holds up a sign in front of the school Monday that says, ''We Want Answers.''

William Byrd administrator Otis Dowdy (left) addresses students who protested outside the school Monday morning. Joe Bradshaw, a student who helped organize the protest, said students need answers about the twitching and want them now.

Photos by Kyle Green | The Roanoke Times

William Byrd juniors Brittany Main (left) and Holly Schlotthober listen to a panel of high school officials, representatives from the Virginia Department of Health and environmental experts talk Monday about the mysterious twitching.

School Superintendent Lorraine Lange takes the microphone Monday to address concerns. She said medical and health department experts have advised school officials there is no need to close William Byrd based on the results of some environmental tests.

Roanoke County school officials have found no environmental cause for the strange twitching symptoms that have affected some students at William Byrd High School, but more testing is planned to begin today.

Two environmental consultants tested air and water quality in the school's art room and elsewhere around the school and detected nothing abnormal, according to the school system. Today, those companies will begin testing surfaces, officials said.

School and health officials have yet to say what they believe is causing the symptoms, which have affected fewer than 10 students. The school system disclosed Monday for the first time that the symptoms include twitching. A parent gave the school officials permission to discuss the child's symptom, after parents at the meeting demanded answers.

The lack of information from the school system has outraged William Byrd parents and students.

On Monday evening, hundreds of students and parents turned out for a meeting with officials from the school system, the Virginia Department of Health and the companies conducting the environmental tests.

Parents repeatedly asked how they were supposed to look out for their children's well-being when they didn't know what to look for.

Dr. Stephanie Harper, district health director for the Virginia Department of Health, told parents to be on the lookout for anything unusual.

"Everything is so vague," one mother, Patti Lafoon, told officials. "You've opened up a plethora of things."

Angela Bradshaw, the mother of a William Byrd sophomore and junior, shed light on the issue when she told parents that the students, as well as a teacher, were experiencing severe headaches, dizziness and seizurelike twitching.

"These kids are scared," Bradshaw said. "They're terrified."

Parents and students implored that the school be closed and classes offered elsewhere.

"There are other alternatives, and you are asking us to send our kids to school while you do your testing," Bradshaw said.

Superintendent Lorraine Lange said that experts with the health department and in the medical field have advised school officials that there is no need to close the school based on the results of the environmental tests.

"If there was even a remote chance there was something wrong with the building, we'd close," Lange said.

Michael Stovall, a member of the Roanoke County School Board, said the board could discuss whether to close the school at its meeting Thursday night.

Parents also were angry that the school didn't notify them about the illness any earlier.

Lange said the school was notified of the first case, which they believed to be isolated, in late September. Then, about a week later, they were alerted to another case. The environmental tests began in mid-October, Lange said.

She said that after the media began covering the symptoms late last week, the school became aware of more cases.

Earlier Monday, about 30 students staged a walkout in protest of the school system's refusal to release details about the situation.

They stood near the school's front entrance, then, after the start of the morning's classes, left school property and crossed the street.

"We need answers, and we want them now," said Joe Bradshaw, a sophomore who helped organize the protest via the social-networking Web site MySpace.

Mackenzie Brewer, also a sophomore, said she does not want to go to school until officials can tell her what is making students twitch.

"There's a disease in our school, and they're not sure what it is, and they're making us go to school," she said.

Several parents who joined in the protest said they were keeping their children home from school. About 280 students were absent Monday, school spokesman Chuck Lionberger said. The school has an enrollment of approximately 1,200 students.

Meanwhile, Vanessa Baxter, the mother of one of the affected students, said a doctor referred her daughter to a neurologist after doing some blood work.

"He said it's a mystery. He doesn't know what's going on," she said, adding that her daughter's symptoms had worsened in the past day.

Both Lionberger and Robert Parker, a spokesman for the Virginia Department of Health, declined to speculate on possible causes.

"Everything is on the table at this point," Parker said. "Nothing has been ruled out."

Studies over the past few years have described similar cases of inexplicable illnesses and symptoms. In many cases, the condition affects young women and may be caused by anxiety or stress, said Elizabeth Whelan, a doctor of public health and epidemiology in New York.

"There's no underlying biological explanation for it," she said. "They may act sick or feel sick, but there's nothing there to biologically explain it."

Staff writer Amanda Codispoti contributed to this report.