Neuropsychological functions in bipolar disorders I and II with and without comorbid alcohol dependence

Bipolar disorder (BP) is a mental disorder most likely to co-occur with substance dependence and abuse, especially alcohol dependence (ALD). Whether the effect of comorbid alcoholism is different between the BP-I and BP-II subtypes remains unclear. We aimed to identify the neuropsychological performance of BP patients with and without comorbid ALD in partial remission from depression or mania, and compare it with that of healthy controls (HCs).

We recruited 29 HCs and 94 BP patients, whom we categorized into four groups: (1) BP-I without a history of alcohol abuse or dependence (BP-I(-ALD); n=22), (2) BP-II without a history of alcohol abuse and dependence (BP-II(-ALD); n=38), (3) BP-I with comorbid ALD (BP-I(+ALD); n=16), and (4) BP-II with comorbid ALD (BP-II(+ALD); n=18). Only males were recruited in this study.

When patients comorbid with ALD were not excluded, there were no significant differences on neuropsychological tests between the BP-I and BP-II groups. However, when patients with comorbid ALD were excluded, there were significant differences between the two BP(-ALD) groups. The BP-I(-ALD) group had lower scores on memory subtests (p≤0.01) than the HC and BP-II(-ALD) groups, but the BP-II(-ALD) and HC groups had similar scores.

We found it important to exclude ALD comorbidity when evaluating neuropsychological functions due to our finding that ALD affected the cognitive performance in BP-I more severely than in the BP-II group. ALD not only impairs neuropsychological function, but also worsen the clinical course and leads to a more pernicious status and negative cycle.