Decrease in genu of the corpus callosum in medication-naïve, early-onset dysthymia and depressive personality disorder

The purpose of this study was to detect differences in regional areas of the corpus callosum (CC) in subjects with early-onset minor depression (dysthymia or depressive personality disorder) and healthy comparison subjects. Based on previous reports that have suggested reduced frontal lobe volume and reduced hemispheric lateralization in the frontal regions of the brain in depression, we hypothesized that the area of the CC that interconnects the frontal regions of the brain, i.e., the genu, will be smaller compared to that of healthy comparison subjects.

Forty female subjects with early-onset dysthymia or depressive personality disorder, as defined by the Structured Clinical Interview for DSM-III-R and the Diagnostic Interview for Depressive Personality, respectively, and age- and gender-matched healthy comparison subjects (n = 42) were recruited (age: 21.4 +/- 2.1 and 20.9 +/- 2.8 years, respectively). All subjects were psychotropic medications-naïve and right-handed. A 1.5T GE Sigma scanner was used to acquire 124 1.5-mm-thick contiguous coronal images. Midsagittal slice images were carefully selected from reconstructed magnetic resonance images both from native and stereotaxic space to measure seven regional areas of the CC.

There were significant diagnosis by CC region interactions [F(6,480) = 4.06, p <.001; F(6,480) = 3.30, p =.003, native and stereotaxic space, respectively]. Early-onset minor depression subjects had a 9.9% (native space) and 6.9% (stereotaxic space) smaller genu of the CC compared to the healthy comparison subjects (the Newman-Keuls post hoc test, p =.005 and.019, native and stereotaxic space, respectively). Early-onset minor depression subjects also had a 7.8% smaller posterior midbody relative to the comparison subjects (the Newman-Keuls post hoc test, p =.033) only in the native space. Severity of current depressive symptoms or duration of illness did not correlate with the size of the genu or the posterior midbody parts of the CC.

These results suggest frontal lobe structural, and possibly functional, abnormalities in the brain in young female adults with a milder spectrum of depression, i.e., DSM-IV early-onset dysthymia or depressive personality disorder. The present findings point out the possible role of frontal lobe abnormality in pathophysiology of early-onset minor depression.