Are there differences in pattern and magnitude of cognitive deficits between euthymic patients with bipolar i and bipolar II disorder?

Background Recent preliminarily evidence suggests that types and severity of cognitive dysfunctions may differ between bipolar disorder I and II (BD-I and BD-II). However, available data are scarce and inconsistent. Aim We aimed to investigate the differences in cognitive deficits between BD-I and BD-II patients. Patients and methods The study included 60 euthymic patients with BD (30 BD-I and 30 BD-II) from a large ongoing project on Egyptian patients with BD; they were compared on the basis of their neuropsychological variables (e.g. executive function, attention, verbal, and visual memory) and compared with 30 healthy controls on cognitive performance. They were subjected to full neuropsychological battery. Results Compared with the healthy controls, patients with BD-I and BD-II showed significant impairment in the majority of cognitive tasks including working memory (digit span backwards, P= 0.000), verbal memory (verbal paired association I and II, P = 0.000), sustained attention (total errors of omission, P = 0.028), and overall executive functions (categories completed, P= 0.000). Post-hoc analysis showed the patients with BD-II having an intermediate level of performance in cognitive functions, between patients with type I disorder and healthy participants, and almost preserved executive functions compared with BD-I patients. Conclusion This study showed differences in severity and pattern of cognitive deficits between BD subtypes, and so the difference is not merely quantitative as confirmed by most of the previous studies. However, there were also qualitative differences in the pattern of executive function deficits, being more extensive in BD-I, which may indicate different biological or genetic etiology between the two BD subgroups. Future researches are needed to support this hypothesis.