Multivariate analysis of bipolar mania: retrospectively assessed structure of bipolar I manic and mixed episodes in randomized clinical trial participants.

BACKGROUND

Manic episodes are heterogeneous. Mixed states may differ in important clinical characteristics from other manic episodes. However, it has not been established whether mixed states are a distinct type of episodes, or a common basic structure exists across manic episodes.

METHODS

Using 2179 well-characterized subjects in the pretreatment phase of six randomized, clinical trials, we conducted rotated factor analysis followed by cluster analysis, using all items from the Young Mania Rating Scale and the Montgomery-Åsberg Depression Scale. Analyses were conducted for all subjects (n=2179) and for those in Diagnostic and Statistical Manual of Mental Disorders - Fourth Edition (DSM-IV) mixed (n=644) and non-mixed (n=1535) episodes separately.

RESULTS

There were five factors characterized (in order of variance accounted for) as depression, mania, sleep disturbance, judgment/impulsivity and irritability/hostility. Cluster analysis identified five clusters. Three were predominately manic, with depression scores below average for the overall group. Two had high average depression scores; these clusters differed in irritability/hostility. Judgment/impulsivity scores were similar across factors. Essentially identical factors and clusters existed whether analyses were done in all subjects or only in subjects classified by DSM-IV as mixed or non-mixed.

LIMITATIONS

Exclusion criteria of studies may limit generalizability of findings.

DISCUSSION

All manic episodes, whether mixed or non-mixed, shared a similar structure according to factor/cluster analysis. Patients with high depression factor scores were heterogeneous with respect to irritability. These data suggest that depressive symptoms should be considered a dimensional property across manic episodes, rather than as defining a specific type of episode.