Evidence of neurobiologic differences between bipolar subtypes

By Hannah Noel, medwireNews Reporter

Taiwanese researchers have found differences in fronto-limbic metabolism and executive function between patients with bipolar disorder (BD) I and II.

In the study, 34 right-handed patients with remitted BD (17 each with BD I and BD II) undergoing treatment and 17 healthy individuals were assessed using fluorodeoxyglucose positron emission tomography (PET) and neuropsychological tests of attention, memory, and executive function.

Tung-Ping Su and team, from the Veterans Hospital in Taipei, found that executive function (calculated using the Wisconsin Card Sorting Test) was significantly worse in BD I patients than BD II patients in all measures.

Specifically, the BD I patients had a higher percentage of errors than BD II patients, at 41.9% versus 28.5%, a lower percentage of conceptual level responses, at 46.9% versus 64.3%, and completed fewer categories, at 3.5 versus 4.6.

The authors also found that patients with remitted BD II fared worse, although not significantly, than healthy individuals in executive function tests.

No differences in attention or memory tests were detected among the groups, however.

Brain PET analysis showed that both BD groups had significantly lower glucose uptake in the bilateral prefrontal areas when compared with the healthy controls.

When comparing subtypes, BD I patients had significantly lower glucose uptake in the bilateral anterior cingulum, striatum, insula, and part of the prefrontal cortex, but higher glucose uptake in the left parahippocampus than their BD II counterparts.

The partial correlation analysis confirmed this, linking higher glucose uptakes in the bilateral prefrontal areas with better executive function. Conversely, in the parahippocampus region, higher glucose uptakes were associated with poorer executive function.

"There are neurobiological differences between subtypes of BD," say Su and team. "BD-I is associated with more impaired fronto-limbic circuitry, which might account for reduced executive function in BD-I patients during remission."

They suggest that the assessment of fronto-limbic dysfunction could prove a useful clinical tool in differentiating BD I from BD II patients in the future.

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