Bipolar disorder patients who have high levels of anxiety during an episode are more likely to have greater long-term depressive morbidity, the results of a US study indicate.

It is known that there are differences between bipolar disorder patients with and without comorbid anxiety, but the long-term prognostic significance of comorbid anxiety is unclear, argue William Coryell, from University of Iowa Hospitals and Clinics in Iowa City, and colleagues.

The team therefore studied 427 participants from the National Institute of Mental Health Collaborative Depression Study who were followed-up prospectively for an average of 17.4 years. The manifestations of anxiety at baseline were characterized and related to the proportion of follow-up weeks in episodes of major depression and mania or hypomania.

Overall, 92 patients had mania only at baseline, while 168 had depression only and 167 were cycling. Using the Schedule for Affective Disorders and Schizophrenia, the researchers found that the patients’ somatic anxiety scores were 1.7, 3.2, and 2.8, respectively, while their psychic anxiety scores were 1.9, 4.0, and 3.5, respectively. The global anxiety level was 3.6, 7.2, and 6.3, respectively.

The percentage of weeks in depressive episodes was not predicted by gender, age at intake, age at illness onset, the presence of antisocial personality disorder, alcoholism, or drug dependence.

Patients with past or future manic episodes spent a smaller percentage of weeks in depressive episodes than those with only episodes of hypomania, at 27.4% and 36.5%, respectively. The proportion of weeks spent in depressive episodes was 13.2% for patients with purely manic episodes at baseline, 37.7% for those who had a purely depressive episode at baseline, and 33.0% for those who had a cycling episode.

Time spent in depressive episodes was not predicted by either panic attacks or any anxiety disorder. However, psychic anxiety was significantly associated with time in depressive episodes, while somatic anxiety had borderline significance.

Global anxiety was found to have a continuous relationship with number of weeks in depressive episodes, with no clear threshold for separating anxious and non-anxious patients.

However, the team was able to determine that patients with a purely manic index episode and a global anxiety level below the median value of 7 spent only 12.4% of weeks in depressive episodes, compared with 18.8% for patients with mania and an anxiety score ?7. The rates for patients with depressed or cycling index episodes were 29.7% and 40.4% depending on whether they had anxiety levels below or above the median, respectively.

The team writes in the American Journal of Psychiatry: “The combination of presenting phase and anxiety level appears to offer a potent clinical tool for predicting whether an individual is likely to follow a course dominated by depressive symptoms or one in which mania is more prominent.

“Such prediction is inherently valuable but may also have practical importance in the selection of a mood-stabilizer regimen designed to offer more protection against one or the other pole of bipolar illness.”

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2009

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