Is bipolar I disorder heterogeneous?

The question whether bipolar I disorder should be subdivided into a preponderantly manic group (M) with no depression or only mild depression (Md) and a nuclear manic-depressive group (MD) has been rarely studied although the problem was raised more than 50 years ago. This paper seeks to elucidate this question by contributing further data.

406 patients with mood disorders hospitalised at some time during the period 1959-1963 were followed-up every five years until 1985; mortality data were collected up to 1997. Data on episodes, outcome, suicides and attempted suicides, alcohol and substance abuse/dependence and long-term medication, as well as on personality (melancholic and manic type) were collected. Major mood disorders were subclassified according to their hospitalisation for depression (D) and/or mania (M).

30 manic patients (M/Md), 130 bipolar I (MD), 60 bipolar II patients (Dm) and 186 major depressive patients (D) were compared. The manic group differed from the bipolar I group in several variables: better school achievement, milder course of the illness (fewer recurrences), significantly less suicidality and a trend to less chronicity and more recovery. Manic patients required less long-term medication than bipolars and they differed in personality types from bipolars, the personality of manic patients being more often of the manic rather than the melancholic type, they were also more aggressive than bipolars. The family history data showed that the overall morbidity risk of first degree relatives of manic patients was significantly lower than that of bipolar patients.

In accord with several other studies our data point to the existence of a more manic (M/Md) group of bipolar subjects. The diagnosis predicts a better course, lower suicidality and fewer and different treatment needs than does nuclear bipolar I (MD) disorder. The M/Md groups, as clinically interesting subgroups of the mood spectrum, should become a target of further research.