Structural Neuroimaging and Neuropathology
Comparisons on a morphometric level are complicated by a lack of informative studies for bipolar disorder (in contrast to schizophrenia). Schizophrenia is considered neurodevelopmental disorder with volume reduction of the whole brain and specific areas (particularly, the hippocampus volume). Bipolar disorder reveals some similar volume reductions in areas such as temporal lobe as well as ventricular enlargement, however, less severely so; convincing evidence for reduction in total brain weight and hippocampus is up to now lacking for bipolar disorder.[37**]
A recent magnetic resonance imaging (MRI)-volumetric analysis reported white matter volume reductions in the left frontal and temporoparietal regions for both disorders, but different locations of gray matter reductions for each of the disorders under discussion. These white matter volume reductions also observed in post-mortem studies for both disorders; in addition, Tkachev et al. reported on the downregulation of key oligodendrocyte and myelination genes for both disorders.
The white matter abnormalities in affected patients in both disorders were apparently not only a sequence of being affected by a specific disorder as they were also present in unaffected relatives, although less severely so; therefore, these abnormalities reflect vulnerabilities.
Cross-diagnostic frontotemporal disconnectivity was concluded from the white matter findings. A consequence might be cognitive impairments; those deficiencies were, indeed, found not only in schizophrenia but also in bipolar disorder - but less severely so.[41**]
The critical period for myelination is the adolescence and early adulthood, namely, the preferential prodromal and early phase of both disorders. Thus, white matter abnormalities might be present before the onset of the disorder and might induce cognitive deficiencies; these were, indeed, observed in children of parents with either of the two diagnoses.[41**]
Another area of cross-diagnostic convergence are GABAergic interneurons; their cell density is decreased in schizophrenia as well as in bipolar disorder. Expression of glutamatergic NMDA receptors is also changed in this subpopulation with possible impact on glutamatergic transmission. Taken together, although volumetric communalities between both disorders are rare, several basic neurobiological processes are shared.
Curr Opin Psychiatry. 2006;19(2):165-170. © 2006 Lippincott Williams & Wilkins
Cite this: Schizophrenia and Bipolar Disorder: Differences and Overlaps - Medscape - Mar 01, 2006.