As a child, Steve Thompson displayed outsized reactions to ordinary events and intense mood swings. By age 12, doctors diagnosed him with bipolar disorder.

The idea that he had a chronic mental illness - one typically marked in adulthood by manic periods followed by depression - frightened him. “It’s something you think you’ll have your entire life,’’ said Thompson, a 23-year-old student at Massasoit Community College in Brockton.

But over the past year, with the help of his longtime psychiatrist, he has weaned himself off mood-altering medication. The result, he said, is a new diagnosis of, at most, mild anxiety.

Patients like Thompson are at the center of a heated debate among child psychiatrists over whether a glaring 40-fold increase within a decade in bipolar diagnoses in children is genuine or the result of routine misdiagnoses.

To address this issue, a panel appointed by the American Psychiatric Association is urging that a new, potentially more transient and less-stigmatizing diagnosis - “disruptive mood dysregulation disorder’’ - be added to the official manual of mental illnesses, which is undergoing a sweeping revision.

The new condition would apply to children who have chronic irritability, as well as recurrent temper outbursts - three or more times a week, on average - that are “grossly out of proportion’’ to the situation the child confronts.

It can be as disabling to a young child as bipolar disorder, but would probably be treated with antidepressants, not antipsychotic drugs. As adults, these children would be more likely to develop anxiety or depression, rather than bipolar disorder.