The role of psychomotor activation in discriminating unipolar from bipolar disorders: a classification-tree analysis

Multiple studies indicate that bipolar disorders are often underrecognized, misdiagnosed, and incorrectly treated. The aim of the present report is to determine which combination of clinical, demographic, and psychopathological factors and corresponding cutoff scores best discriminate patients with unipolar disorder from those with bipolar disorders.

The study sample includes outpatients and inpatients (N = 1,158) participating in 5 studies carried out in the United States and Italy between October 2001 and March 2008, one of which was a randomized clinical trial. Diagnostic assessment was carried out with the SCID, which allows diagnoses to be made according to DSM-IV-TR criteria. Using an exploratory statistical approach based on a classification tree, we employed 5 mania spectrum factors and 6 depression spectrum factors derived from the Mood Spectrum Self-Report Instrument (MOODS-SR) in combination with demographic and clinical characteristics to discriminate participants with unipolar versus bipolar disorders.

The psychomotor activation factor, assessing the presence of thought acceleration, distractibility, hyperactivity, and restlessness for 1 or more periods of at least 3 to 5 days in the lifetime, identified subgroups with an increasing likelihood of bipolar disorder diagnosis. Mixed instability and suicidality contributed to further subtyping the sample into mutually exclusive groups, characterized by a different likelihood of receiving a diagnosis of bipolar disorder. Of the demographic and clinical characteristics included in the analysis, only sex proved to be useful to improve the discrimination.

The psychomotor activation factor proved to be the most potent discriminator of those with unipolar versus bipolar diagnoses. The items that constitute this factor, together with those that constitute the mixed instability, suicidality, and euphoria factors, might be useful in making the differential diagnosis.