The number of young people diagnosed with bipolar disorder has risen 40-fold in recent years, according to a new study. But the authors themselves question the accuracy of the diagnoses.

The researchers say there are two possible reasons for the huge spike in bipolar disorder diagnoses in the young: Either the disorder was historically underdiagnosed in children and teens and is now being better recognized; or bipolar disorder is currently being overdiagnosed in this age group.

"Without independent systematic diagnostic assessments, we cannot confidently select between these competing hypotheses," the researchers note.

Dr. Mark Olfson, of Columbia University and New York State Psychiatric Institute, and his colleagues looked at increases between 1994-1995 and 2002-2003 in doctor's office visits that ended with a diagnosis of bipolar disorder among American youths aged 19 and younger.

They found that outpatient visits with a diagnosis of bipolar disorder in the younger age group increased approximately 40-fold, from 25 per 100,000 people in 1994-1995, to 1,003 per 100,000 in 2002-2003. During the same time, the diagnosis of bipolar disorder in adults increased nearly two-fold, from 905 to 1,679 per 100,000.

The study is published in the Archives of General Psychiatry.

Bipolar disorder, also called manic depression, is characterized by extreme mood swings. Long periods of depression can suddenly be followed by episodes of mania, which are periods of boosted energy and restlessness that can last for a week or more. The causes of bipolar disorder are uncertain but the illness tends to run in families.

Some doctors do not believe that bipolar disorder exists among children while others think it is frequently misdiagnosed as ADHD, anxiety disorders or simple depression. In children, extreme irritability and disruptive behaviour are often the main symptoms.

Olfson's team also found that the vast majority of youth and adults were prescribed medication at the time of diagnosis of bipolar disorder, including mood stabilizers, antipsychotics and antidepressants.

The researchers warn there is "an urgent need" to evaluate the safety of drugs commonly used to treat young people with bipolar disorder, since most medications were approved for adults and have not been well-studied in children.