Is cognitive decline significant in bipolar I?

Professor Carla Torrent began by highlighting several recent meta-analyses that support the presence of cognitive impairments in individuals with euthymic bipolar disorder.

In a systematic review¹ referred to by Prof Torrent that compared cognitive impairment between schizophrenia and bipolar disorder, the prevalence was higher in schizophrenia (85-100) compared to bipolar disorder (40-60%).

Interestingly, higher cognitive impairment was related to a higher number of manic episodes and was more significant in bipolar I than bipolar II. It was also increased in patients with a history of psychotic symptoms. Available treatments didn’t seem to change cognition in either group.

SAD vs bipolar patients

Similarly, SAD patients also fared worse than bipolar patients, as revealed in another paper² presented by Prof Torrent. SAD patients showed more impairment than bipolar patients on tests of attention, psychomotor speed and memory but there were not significant differences on measures of cognitive flexibility.

Bipolar vs schizophrenia

The next study compared neurocognitive dysfunction in bipolar and schizophrenia sprectrum disorders and demonstrated that neurocognitive dysfunction seems to be determined more by history of psychosis than diagnostic categories or subtypes³.

During this session it was evident (and not entirely surprising) that cognitive deficits in bipolar disorder are milder when compared to schizophrenia but less obvious is that they are qualitatively similar to those of patients with schizophrenia.

5 conclusions

Professor Torrent concluded with a round-up of what the evidence suggests thus far:

1. Schizophrenia and bipolar disorder show greater phenotypic similarity in terms of the nature than severity of their neuropsychological deficits
2. Cognitive performance in groups of psychotic patients may be influenced by the degree to which they are symptomatic at the time of testing (8-12 weeks of remission before testing.)
3. One possible reason for the divergent findings between SAD vs BD may be the presence or absence of psychotic symptoms in BD
4. The history of psychosis may be more influential in determining neurocognitive dysfunction than diagnostic category or subtype
5. Findings suggest that SZ, SAD and BDP are on a neurobiological continuum

Functional imaging

In an interesting following talk, the next speaker Dr Mercи Madrelooked at functional imaging results. Dr Madre concluded that even though so far no direct comparison of functional imaging results between schizophrenia, bipolar and schizoaffective disorder have been published, results in schizoaffective disorder seem similar to those of bipolar disorder and schizophrenia, supporting the idea that all three illnesses share the default mode network dysfunction as what is most probable a trait-like abnormality.

Thus, brain structural and functional neuroimaging results are suggestive for a brain dysfunction that might support an overlap between schizophrenia, bipolar and schizoaffective disorder, contrary to the view of schizoaffective disorder as a separate pathology.