ADHD increases major depression to bipolar disorder conversion

By Lucy Piper, Senior medwireNews Reporter

Young people with major depression have an increased risk of conversion to bipolar disorder if they have comorbid attention deficit/hyperactivity disorder (ADHD), suggest findings from a longitudinal follow-up study.

The results showed that 1193 individuals with major depression and comorbid ADHD were 1.5 times more likely to develop subsequent bipolar disorder than 56,830 individuals with major depression alone.

The patients with comorbid ADHD were, on average, 6 years younger at the time major depression was diagnosed than their major depression-only counterparts. And the comorbidity was associated with a significantly increased risk of diagnostic conversion to bipolar disorder in both men (hazard ratio [HR]=1.34) and women (HR=1.85) and irrespective of whether patients developed major depression as an adolescent (HR=1.41) or a young adult (HR=2.11).

The study participants, who were younger than 30 years of age, were identified through the Taiwan National Health Insurance Research Database and were enrolled between 2000 and 2008, with bipolar disorder onset monitored until the end of 2011.

Bipolar disorder was significantly more common in patients with major depression and ADHD than in those with major depression alone, with incidences of 18.9% versus 11.2%. And it occurred earlier, at an average age of 22.3 years versus 25.2 years.

The findings, published in Bipolar Disorders, showed that the rate of conversion from major depression to bipolar disorder before adulthood (<18 years old) was significantly higher among adolescents with comorbid ADHD, at 6.9% compared with 6.3% for those without ADHD. The rate of conversion in adulthood was also greater for those with comorbid ADHD, at 6.3% versus 5.2%.

The increased risk of bipolar disorder conversion associated with comorbid ADHD was independent of age, gender, socioeconomic status and other psychiatric comorbidities.

ADHD was not the only independent risk factor for subsequent bipolar disorder, however; others included disruptive behaviour disorders, substance and alcohol use disorders and anxiety disorders.

Researcher Tung-Ping Su (Taipei Veterans General Hospital, Taiwan) and colleagues note that this is in line with previous findings and evidence suggesting an association between ADHD and mood dysregulation and bipolar disorder.

But they say that “[f]urther studies would be required to investigate the underlying mechanisms between ADHD comorbidity and diagnostic conversion from major depression to bipolar disorder.”

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