PITTSBURGH — Patients with bipolar II disorder are at high risk for alcohol abuse and dependence, based on findings from a 20-year, longitudinal study with about 600 patients.
The study's findings also suggest that bipolar II disorder can be more broadly defined than current DSM-IV criteria, Kathleen R. Merikangas, Ph.D., said at the Sixth International Conference on Bipolar Disorder.
Men and women in this study who developed bipolar II disorder using DMS-IV criteria were 4.6-fold more likely also to develop alcohol abuse, compared with people in the study who did not develop mood disorders.
The bipolar patients were also 8.2-fold more likely to be alcohol dependent, compared with those without a mood disorder. Those rates of alcohol abuse and dependence were substantially higher than for people in the study who had major depression of symptoms or mania but no bipolar disorder.
“It looks like alcohol is the drug that patients with bipolar disorder use,” said Dr. Merikangas, chief of the section on developmental genetic epidemiology at the National Institute of Mental Health.
She hypothesized that “bipolar patients drink when they're manic. Mania is not a pleasant state. It's marked by agitation and restlessness. Alcohol calms them down.” But she stressed that that explanation for the high rate of alcohol use by bipolar patients needs confirmation.
The substance abuse and dependence in the bipolar patients appeared to be specific for alcohol, she said at the conference, which was sponsored by the University of Pittsburgh. A similar analysis found no increased risk for cannabis use or dependence in bipolar patients.
The study has been a collaboration between researchers at the National Institute of Mental Health and the University of Zurich. In 1978, more than 4,500 men aged 19 years and women aged 20 years were screened for the Zurich cohort study.
The men had registered for the Swiss draft, and the women had registered for work permits. The group was screened for risk factors for bipolar disorder, and two groups were selected for ongoing assessment over the following 20 years. One group had high symptom scores that showed they faced an increased risk of eventually developing bipolar disorder. A second group with low scores was also included to serve as controls.
A total of 591 people was selected for long-term follow-up, which involved periodic interviews. By 1999, after 20 years of follow-up, 367 people remained in the study.
Three different criteria were used to identify people with bipolar disorder. DSM-IV criteria were the most restrictive, requiring people to have at least three symptoms of bipolar disorder that each lasted at least 4 days. After 20 years of follow-up, 12 people had developed bipolar II disorder based on the DSM-IV criteria.
The Zurich strict criteria also required three symptoms, but they could last 1 day or longer to count toward a diagnosis. Also, the symptoms had to have consequences, such as impairment of life activities. By the Zurich strict criteria, 33 people from the group were diagnosed with bipolar disorder.
The Zurich broad criteria required that people have only two symptoms that each lasted for at least 1 day, and consequences of the symptoms were not necessary. By the broad criteria, 44 people eventually developed bipolar disorder during 20 years of follow-up.
In addition, 96 people were diagnosed with monopolar major depression using DSM-IV criteria.
Several analyses that compared the three definitions of bipolar disorder and monopolar depression confirmed that the broad Zurich definition was a reasonable way to identify patients with bipolar disorder. For example, the percentage of patients with a family history of mania was 25% among those who met the DSM-IV criteria for bipolar disorder, 6% of those who met the strict Zurich criteria, 18% of those who met the broad Zurich criteria, and 4% of those who were diagnosed with monopolar depression.
The broad definition of bipolar disorder appeared valid, because people who met the broad criteria showed consistent similarities with patients who met the DSM-IV criteria, Dr. Merikangas said.