Impulsivity as a trait characteristic is increased in bipolar disorder and may be a core factor of the illness. We have investigated relationships between trait-like impulsivity, measured by the Barratt Impulsiveness Scale (BIS-11), and demographic and illness-course characteristics of bipolar disorder. We studied 114 subjects with bipolar disorder and 71 healthy comparison subjects. Diagnoses were based on the Structured Clinical Interview for DSM-IV. In addition to impulsivity, we examined age, education, gender, psychiatric symptoms, and characteristics related to course of illness. We used general linear mixed model analysis to evaluate the manner in which the variables contributed to BIS-11 scores. All BIS-11 subscale scores were higher in bipolar disorder than in comparison subjects. There were less consistent independent effects of education and age. Elevated BIS-11 scores were associated with early onset, more frequent episodes of illness, and a history of suicide attempts. These relationships persisted when age, gender, and education were taken into account. These results show that, after accounting for common confounding factors, trait-like impulsivity was substantially higher in subjects with bipolar disorder than in nonbipolar comparison subjects, regardless of symptoms. Within subjects with bipolar disorder, high trait impulsivity was associated with a more severe course of illness.
