Conversion from psychotic depression to bipolar disorder explored

By Joanna Lyford, Senior medwireNews Reporter

Danish researchers have identified a range of characteristics in people with psychotic depression that predict an increased risk for conversion to bipolar disorder.

“This conversion has important implications for the choice of treatment,” they note in Bipolar Disorders.

The researchers analyzed data from several Danish registries to identify conversion to bipolar disorder among patients with an initial diagnosis of unipolar psychotic depression between January 1995 and December 2007.

Among the 8588 patients included in the study, 609 were diagnosed with bipolar disorder (defined as a new diagnosis of hypomania, mania, mixed affective episode, or bipolar disorder) during follow-up, giving a conversion rate of 7.1%.

This rate is lower than that reported in other longitudinal studies, note the authors, and is probably explained by methodologic issues.

Comparison of patients who did and did not convert to bipolar disorder identified a range of differences, seven of which emerged as significant risk factors in multiple logistic regression analysis.

These were: younger age at onset of unipolar psychotic depression (adjusted odds ratio [AOR]=0.99 per year of increasing age); recurrent depression (AOR=1.02 per episode); living alone (AOR=1.29); receiving a disability pension (AOR=1.55); and the highest educational level being a technical education (AOR=1.55), short-cycle higher education (AOR=2.65), or medium-cycle higher education (AOR=1.75).

Further analysis of the impact of age at psychotic depression onset found that, compared with people aged 20 years or younger at onset, the AOR for bipolar disorder was 1.64 for those aged 20–29 years, 1.58 for age 30–39 years, 1.80 for age 40–49 years, 1.36 for age 50–59 years, 1.19 for age 60–69 years, 0.85 for age 70–79 years, and 0.40 for age 80 years or older.

Thus, the risk was “less dose-dependent than expected,” say Søren Østergaard (Aalborg University Hospital, Denmark) and colleagues. However, the risk for converting to bipolar disorder is likely underestimated in this study, again due to methodologic issues, they say.

Noting that conversion to bipolar disorder has implications for the choice of treatment and for prognosis, the team concludes: “This knowledge should be taken into account by clinicians monitoring the treatment of patients with [psychotic depression].”

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