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The number of US people aged under 20 years who received a diagnosis of bipolar disorder increased 40-fold from 1994 to 2003, a new study says. It also found that the number of diagnoses among adults almost doubled in the same period.
The study reported that between 1994 and 2003 the number of visits to US doctors in which young people were given a diagnosis of bipolar disorder or received treatment increased from 25 in every 100000 people in the population to 1003 per 100000 (Archives of General Psychiatry 2007;64:1032-9). The number of diagnoses among adults aged over 20 rose from 905 to 1679 per 100000.
The authors wrote, “Either bipolar disorder was historically underdiagnosed in children and adolescents and . . . the problem has now been rectified, or bipolar disorder is currently being overdiagnosed in this age group.”
The study's lead author, Mark Olfson, clinical professor of psychiatry at the New York State Psychiatric Institute at Columbia University, said that during the study period the standard reference book on psychiatric disorders for US doctors, the Diagnostic and Statistical Manual of Mental Disorders, had liberalised its criteria for diagnosing bipolar disorders and had included bipolar II disorder in its criteria.
The only drug approved by the US Food and Drug Administration to treat bipolar disorder in children during the study period was lithium, but new drugs to treat the disorder in adults were introduced, and doctors may have used them “off label” in children as part of the trend to greater use of psychotropic drugs, Dr Olfson said.
Bipolar disorder in young people also attracted media attention over this period.
The study was based on the US national ambulatory medical care survey. This survey covers patients with medical insurance who visited office based doctors during a particular week each year and so does not include patients who may have visited community mental health clinics, hospital outpatient clinics, or other sources of help.
Dr Olfson said that bipolar disorder most often begins in late adolescence or early adulthood but that it usually takes about six years before a diagnosis is made. In adults about two thirds of patients with the disorder are women, but in this study two thirds of those whose illness was diagnosed before they were 20 were men.
Comorbidity, overdiagnosis, and misdiagnosis may have contributed to the high number of diagnoses of bipolar disorder in young people, the study says. Dr Olfson said that comorbidity with attention deficit hyperactivity disorder and other disorders was common in children. He said that irritability was a common symptom of bipolar disorder but also of many other disorders and may even be part of adolescence, leading to confusion in diagnosis.
The study reports patterns in diagnosis rather than patterns in the prevalence of the disorder after treatment, the authors say. Other studies may determine the accuracy of clinical diagnoses of childhood bipolar disorder in clinical practice, they write.