Bipolar subtypes show neurobiologic differences

Results from a Taiwanese study show that there are significant neurobiologic differences between patients with bipolar (BD) I and II disorder.

The team found that remitted BD I patients had altered patterns of glucose uptake in several brain regions compared with BD II patients.

The findings "might account for reduced executive function in BD I patients during remission," comment Tung-Ping Su (Taipei Veterans General Hospital) and colleagues in Bipolar Disorders.

The researchers studied 17 remitted patients with BD I, 17 remitted patients with BD II, and 17 age-, education-, and handedness-matched mentally healthy controls.

All of the participants underwent fluorodeoxyglucose positron emission tomography (PET) scans of the brain and completed neurocognitive tests of attention, memory, and executive function.

The researchers found that BD I patients had significantly poorer executive function than BD II patients and controls, as indicated by a higher percentage of errors (41.9 vs 28.5 and 20.6%), a lower percentage of conceptual level responses (46.9 vs 64.3 and 75.8%), and fewer categories completed (3.5 vs 4.6 and 5.8) on the Wisconsin Card Sorting Test. The difference between BD II patients and controls was not significant.

There were no significant differences among the groups regarding scores on tests of attention and memory.

Both groups of BD patients showed significantly lower glucose uptake than controls in the bilateral prefrontal areas (the dorsolateral and medial prefrontal cortex), the cingulate cortex, the thalamus, and the bilateral inferior frontal gyri extending to the anterior insula and temporal poles.

Furthermore, BD I patients had significantly lower glucose uptake than BD II patients in the bilateral insula, the striatum, the anterior cingulate cortex, the right dorsolateral prefrontal cortex, and significantly higher glucose uptake in the left parahippocampus and left middle temporal gyrus.

"Taken together with the findings of worse performance on executive function tests in remitted BD I patients versus BD II patients and healthy subjects, these findings suggest that the loss of executive function ability in BD I patients could be attributable to frontal-limbic dysfunction," Su et al conclude.

They add: "Our findings support the hypothesis of a neurobiological difference between subtypes of BD."

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