Social, physical clues signal eating disorders: psychopathology often consists of preoccupations and rituals, such as excessive mirror checking.

NEW YORK -- When diagnosing adolescents with eating disorders, be aware that they may try to trick you to avoid admitting their behavior, one expert says.

"These kids go on the Internet and they know the diagnostic criteria--often better than the psychiatrist," Dr. Katherine A. Halmi, professor of psychiatry at Weill Cornell Medical College in New York, said at the annual meeting of the American Society for Adolescent Psychiatry.

"They know all the mechanisms for how to fool you."

That makes conducting a careful interview with both the adolescent and the family members critical, she said.

Be suspicious of eating disorders in adolescents with marked weight fluctuations or significant weight loss, Dr. Halmi advised. It also is important to look for excessive levels of activity such as constant jogging, biking, and aerobic exercise.

These adolescents often will pace around the house and never seem to sit down, she said.

The family and patient interviews should also include thorough questions about purging behaviors--self-induced vomiting, laxative abuse, diuretic abuse, and enemas.

But keep in mind that sometimes the parents choose to ignore this behavior or may not know about it, Dr. Halmi said.

For example, the psychiatrist often ends up seeing the family because the adolescent's friends have called the parents to alert them to the problem.

The core eating disorder psychopathology often consists of preoccupations and rituals. All teenage girls look in the mirror frequently, Dr. Halmi said, but when this behavior becomes excessive, become concerned.

Other common preoccupations among adolescents with eating disorders include fear of getting fat, frequent weighing, calorie counting, and excessive concern about the fat content and other ingredients in foods.

Anorexic patients who are underweight might develop a preoccupation with food. Some times adolescents with anorexia actually collect recipes and cook for their families.

However, these patients will refrain from eating, according to Dr. Halmi.

Many patients with bulimia have a fear of not being able to stop eating. Frequently, they will stop eating with family members and become more and more isolated, she said.

Clinicians also can look for physical signs to diagnose eating disorder behavior. When looking to confirm purging behavior in an adolescent, perform a blood analysis, Dr. Halmi advised.

If the adolescents are purging, they will have an elevated serum amylase level, and if they are purging repeatedly this will be especially prominent.

Bulimia nervosa is frequently diagnosed by a dentist, because of the telltale physical signs such as tooth erosion and poor gum hygiene.

Swollen parotid glands and scars on the dorsum of the hand also are indications of bulimia.