Bipolar Disorders: Mixed States, Rapid-Cycling, and Atypical Forms

97 Bipolar I and bipolar II: a dichotomy?patients and that there might be pathophysiological differences between bipolar Iand bipolar II.Differences have been found between bipolar I and II disorders on magneticresonance imaging scanning and on the presence of vascular abnormalities,including Raynaud’s phenomenon, migraine, and migraine equivalents (Ferrieret al., 2001). Endicott (1989) found a positive correlation between bipolarity anda cluster of disturbances, including classic migraine headache, the peripheralvascular disturbance of Raynaud’s disease, enuresis, vague episodic phenomenasimilar to migraine prodrome, fingernail biting, and learning disorders; most ofthe psychophysiological conditions showed a higher incidence in bipolar IIpatients with respect to bipolar I patients.By contrast, periventricular hyperintensities have been reported to be morecommon in bipolar I patients than in bipolar II patients and normal comparisonsubjects (Altshuler et al., 1995). It would be necessary to increase the number ofbrain-imaging studies that separate bipolar I from bipolar II patients to knowwhether a pathophysiologic brain marker could distinguish between bipolar I andbipolar II disorders.There were no quantitative magnetic resonance imaging studies of bipolar IIpatients until Hauser et al. (2000) measured temporal lobe and ventricular structuresin bipolar I, bipolar II, and control subjects. Their results showed that therewere no differences in temporal lobe or hippocampal volume estimates in the thirdventricle area and lateral ventricle-to-cerebrum area ratio among diagnosticgroups. The lateral ventricle area and the lateral ventricle-to-cerebrum area ratiowere significantly larger in bipolar I patients than either bipolar II patients orcontrol subjects only in the left hemisphere. Furthermore, these measures wereapproximately twice as large in the bipolar I patients as in the other groups. Thisstudy concluded that bipolar I disorder, particularly in males, might show differentneurobiological alterations compared to bipolar II or control subjects.Positron emission tomography was used in a recent study by Berns et al.(2002)todetermine whether patients with bipolar II disorder had altered regional brainresponses to novel motor sequences with respect to healthy subjects. The resultsshowed that, in the comparison subjects, a spatial attention circuit in the superiorparietal lobe and supplementary motor area was activated in response to the introductionof the new sequence. Bipolar II patients did not display this activation pattern;instead, a widespread limbic network was activated in response to the new sequence.Future neuroimaging research should study comparative functional neuroimagingwith single-photon emission computed tomography and positron emissiontomography of bipolar I disorder and bipolar II disorder. Neuroimaging could beuseful in validating diagnostic subtypes, although the results to date are toounspecific (Benabarre et al., 2002).