More support for interhemispheric disconnectivity in bipolar disorder

A UK study supports a role for interhemispheric disconnectivity in bipolar disorder, showing reduced corpus callosum area and thickness in patients with the condition.

The researchers, led by Adrian Lloyd (Newcastle University), also found reduced signal intensity in women with bipolar disorder, relative to mentally healthy women.

The team assessed magnetic imaging data on 48 euthymic patients (23 men) with bipolar disorder diagnosed an average of 19.2 years earlier, and 46 mentally healthy controls (19 men) matched for age, gender and social/occupational class.

They found that, for Witelson-defined callosal areas, bipolar disorder patients had significant size reductions for subregions 1, 2, 5, 6 and 7 and for the corpus callosum overall.

For Denenberg-defined callosal widths, bipolar disorder patients had significant reduction in areas corresponding with the genus, midbody and isthmus and splenium. Lloyd et al note that these areas approximate to the Witelson areas with the most significant reductions (areas 2, 5 and 6), and are in line with findings from previous studies.

The results suggest that “parts of the corpus callosum that connect with prefrontal and temporal/parietal cortex are those most affected by bipolar disorder”, they write in TheBritish Journal of Psychiatry.

Callosal signal intensity was lower in men than women in both the patient and control groups. However, women with bipolar disorder had significantly lower signal intensity than control women, whereas there was no difference for men.

This implies additional changes in the corpus callosum of female bipolar disorder patients, possibly related to sex hormones, says the team.

“Ideally, longitudinal studies of callosal structure and function are needed to track progression of changes between adolescence and adulthood and between episodes of acute illness and euthymia,” say Lloyd et al.

But they suggest: “In the absence of longitudinal studies there may be merit in comparing callosal changes between adults who have had onset of illness before and following completion of callosal myelination in the mid-20s with combined structural, diffusion and functional imaging modalities.”

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