Researchers in the United States are saying that Intermittent Explosive Disorder (IED) often known as Road Rage, may be far more common than previously thought.

The condition which causes people to react violently often for no apparent reason, is vastly under-diagnosed, say the U.S. researchers and they believe as many as 16 million Americans have been affected by IED in which the sufferer displays an inappropriate level of violence.

According to the Diagnostic and Statistical Manual of Mental Disorders, IED attacks are out of proportion to the social stressors triggering them and are not due to another mental disorder or the effects of drugs or alcohol.

As a rule people with the disorder overreact to situations with uncontrollable rage, feel a sense of relief during the angry outburst, and then feel remorseful about their actions.

According to researchers from Harvard Medical School and Chicago University 4% of the US population have severe IED which is manifested with three or more outbursts a year.

Although IED is a clearly defined and accepted mental disorder it was always unclear how many people might be affected.

Study author Emil Coccaro MD, the Ellen C. Manning professor and chair of the Department of Psychiatry at the University of Chicago Pritzker School of Medicine, says if people explain such explosive outbursts as just bad behaviour, they are not accepting the problem is a serious biomedical one which can be treated.

In order for a person to be diagnosed with IED they must have had three episodes of impulsive aggressiveness which are grossly out of proportion to the situation, such as that seen in cases of road rage or domestic violence, where control is suddenly completely lost and the person breaks or smashes something, hits or tries to hurt someone, or threatens to hurt someone.

For the research the team assessed the results of a national face-to-face survey, the ‘National Comorbidity Survey Replication’, of 9,282 U.S. adults carried out between 2001 and 2003 in conjunction with the World Health Organization World Mental Health Survey Initiative.

They found that 7.3% of the population could be classed as having IED, a much higher rate than previously estimated and around eight million adults had the most severe form of IED, with much more frequent outbursts.

It is suggested that the average person with IED will carry out 43 attacks, and the condition appears to first manifest itself during adolescence, with the average age of the first episode found to be 13 for males and 19 for females.

Although most study respondents had seen a professional in order to deal with emotional problems, only 12% had been treated for their anger in the past 12 months and only 29% of people had ever received treatment for the condition.

Among people with this disorder, 81.8 percent also were diagnosed with depression, anxiety, and alcohol or drug abuse disorders.

Study leader Ronald Kessler, PhD, professor of health care policy at Harvard Medical School, says IED is not a clinical term well-known in society, but the weight of these numbers should help patients and physicians recognise the pervasiveness of the disorder and develop appropriate treatment strategies.

The researchers suggest that identifying the condition early on through violence prevention strategies in schools and providing appropriate treatment, might prevent problems such as alcohol and drug dependency and depression, which are associated with the disorder, appearing later in life.

Coccaro says effective treatment for IED includes both behavioral and pharmacological interventions (selective serotonin reuptake inhibitors and mood stabilizers) but ideally, people should be treated with both drugs and cognitive-behavioral therapy.

He says drugs increase the threshold at which people will explode, and cognitive-behavior therapy teaches people how to handle the feelings of frustration or threat that often lead to the explosive episodes.

The report is published in the current issue of the Archives of General Psychiatry.