Recurrent, unwarranted blow-ups such as road rage may have a biological basis, according to a new study.

Blood tests of people who display the hostile outbursts that characterize a psychiatric illness known as intermittent explosive disorder show signs of inflammation, researchers say.

"What we show is that inflammation markers [proteins] are up in these aggressive individuals," said Dr. Emil Coccaro, professor and chair of psychiatry and behavioral neuroscience at the University of Chicago.

Currently, medication and behavior therapy are used to treat intermittent explosive disorder, which affects about 16 million Americans, according to the U.S. National Institute of Mental Health. But these methods are effective in fewer than 50 percent of cases, the study authors noted.

Coccaro now wants to see if anti-inflammatory medicines can reduce both unwarranted aggression and inflammation in people with this disorder.

Meanwhile, he said, it's important for those with the condition to seek treatment, rather than expect loved ones and others to live with the episodes of unwarranted hostility.

Experts began looking at inflammation and its link to aggressive behavior about a decade ago, Coccaro said. The new research, published online Dec. 18 in JAMA Psychiatry, is believed to be the first to show that two indicators of inflammation are higher in those diagnosed with the condition than in people with other psychiatric disorders or good mental health, he said.

The body-wide inflammation also puts these people at risk for other medical problems, including heart attack, stroke and arthritis, Coccaro noted.

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Still, it's not known if inflammation triggers aggression or if repeated acts of aggression lead to inflammation, Coccaro said. Although the two are linked, the study does not establish a cause-and-effect relationship.

Initial controversy about whether intermittent explosive disorder is a "real" illness has subsided as more research has been done, Coccaro added.

Those diagnosed with the condition have episodes of impulsivity and aggression that are way out of proportion to the stressor. They lose control, breaking property or trying to hurt people. For example, they might blow up at a store clerk for moving too slowly or making a minor mistake.

For the study, Coccaro looked at levels of two types of indicators of inflammation in blood: C-reactive protein and interleukin-6. Elevated levels of these proteins have been linked with aggressive and impulsive behaviors in people and animals.

Nearly 200 people participated in the study. Sixty-nine had intermittent explosive disorder, 61 had psychiatric disorders not involving aggression and 67 were in good mental health.

"The levels of chronic inflammation are about twice as great in [intermittent explosive disorder] compared with healthy subjects," Coccaro found.

The blood test to evaluate inflammation won't be a diagnostic test, however, because the disorder is diagnosed by observation and reports of behavior.

Mark Dombeck, a psychologist in Oakland, Calif., said the new study is interesting even though it has no immediate clinical application. "It's not possible to say whether the inflammation is contributing to the aggression or whether the aggression is contributing to the inflammation," he agreed.

But even if inflammation is eventually found to be a cause of intermittent explosive disorder, Dombeck said it still may not lead to a simple solution. "Behavior is certainly influenced by biology, but it's influenced by a lot more than that," he explained.

Eliminating the cause of a disorder, he noted, is not always enough to change the behavior once it is established.

More information

To learn more about intermittent explosive disorder, visit the U.S. National Institutes of Health.

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