Reduced posterior corpus callosum area in suicidal and non-suicidal patients with bipolar disorder

Impulsivity is a characteristic of bipolar disorder (BD) that can contribute to the risk for suicidal behavior. Evidence suggests that gray and white matter abnormalities are linked with impulsivity, but little is known about the association between corpus callosum (CC) and impulsivity in BD. We examined the CC area and impulsivity in euthymic bipolar I patients, with and without lifetime history of suicide attempts, and in healthy controls.

Nineteen bipolar patients with a suicide attempt history (BP-S), 21 bipolar patients without suicide attempt history (BP-NS), and 22 healthy controls (HC) underwent clinical assessment by the Structured Clinical Interview with the DSM-IV axis I (SCID-I), the Barratt Impulsiveness Scale (BIS-11), and MRI scan.

No differences were observed for any CC subregion between BP-S and BP-NS groups. There was a significant reduction in the genu (p=0.04) and isthmus areas (p=0.01), in bipolar patients compared with HC. In the BP-S group, the BIS-11 total (p=0.01), attention (p=0.001) and non-planning (p=0.02) impulsivity scores were significantly higher than in the BP-NS and HC groups.

These results cannot establish causality because of the cross-sectional nature of the study.

This report potentially provides evidence that a reduction in the CC area is present even in non-symptomatic bipolar patients, which may be evidence of a biological trait marker for BD. Furthermore, the study demonstrated that BP-S group had higher impulsivity even during euthymia, which points to a sustained association between lifetime history of suicide attempts and impulsivity in BD.