Certain cognitive deficits worse in BDI than BDII patients
MedWire News: Patients with bipolar I disorder (BDI) show greater memory and semantic fluency deficits than those with bipolar II disorder (BDII), but both patient groups show similar impairments in other measures of cognition, results from a review and meta-analysis of published studies show.
Writing the journal Acta Psychiatrica Scandinavica, Emre Bora (University of Melbourne, Victoria, Australia) and colleagues explain: "The clinical distinction between BDII and BDI is not clear-cut."
But they add that "cognitive functioning offers the potential to explore objective markers to help delineate this boundary."
To investigate possible differences in cognition between BDI and BDII patients, the researchers searched the literature for all relevant studies published between 1987 and July 2009.
In total, 12 studies, with or without a mentally healthy control group, met criteria for inclusion in the final analysis.
The participants' cognitive abilities were assessed using a variety of tests, including the California verbal learning test, the trail making test, the Rey Auditory Verbal Learning Test, the Tower of London test, the Wechsler Memory Scale, the Stroop interference task, and the Wisconsin Card Sorting Test.
For each cognitive test, an effect size and standard error was calculated. Effect sizes for each cognitive variable were calculated as the mean difference between BDI and BDII patients divided by the pooled standard deviation.
The researchers found that patients with BDII were significantly less impaired than those with BDI on measures of verbal memory, with an effect size of 0.52.
BDII patients were also less impaired than BDI patients on measures of visual memory and semantic fluency, with effect sizes of 0.38 and 0.46, respectively.
However, there were no significant differences between the two patients groups in other cognitive domains, such as attention, planning and reasoning, working memory, or global cognition.
Both patients groups performed worse than mentally healthy controls in all cognitive domains, the researchers note.
Bora et al conclude: "Our findings revealed a different profile for certain cognitive deficits between BDI and BDII, suggesting that there might be some neurobiological differences that underpin these subtypes of BD."
They add: "Further studies are needed to investigate whether more severe deficits in BDI are related to neurotoxic effects of severe manic episodes on medial temporal structures or neurobiological differences from the onset of the illness."
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By Mark Cowen