Bipolar disorder is a chronic mood disorder with episodic progress and high relapse rate. Growing evidence suggests that individuals with bipolar disorder display cognitive impairment which persists even throughout periods of symptom's remission.
137 bipolar patients met the inclusion criteria (depressive episode: DSM-IV-TR criteria for major depressive episode, HAMD score ≥17; manic/hypomanic episode: DSM-IV-TR criteria for manic/hypomanic episode, YMRS score ≥12, euthymic: 6 months of remission, HAMD score ≤8, YMRS score ≤6; and mixed: DSM-IV-TR criteria for mixed episode, HAMD score >8 and YMRS score >6) and were therefore enrolled in the study. Patients were free of psychotic symptoms (hallucinations/delusions) at the moment of testing. Control group consisted of 62 healthy subjects without history of neurological and/or psychiatric disorder. Cognitive battery has been applied in order to assess verbal memory, working memory, psychomotor speed, verbal fluency, attention and speed of information processing, and executive function. Following data were collected: demographics, psychiatric history, age of illness onset; current and previous treatment (including hospitalizations). Cognitive deficits were assessed in bipolar patients experiencing manic, depressive, mixed episodes or who were euthymic in mood. Results were compared between the subgroups and with healthy individuals. The association of impaired cognition with illness course was analyzed.
Bipolar patients showed cognitive deficits in all evaluated domains when compared to controls. The lowest scores were obtained for the verbal fluency test. After adjusting for current episode, manic subgroup showed greater cognitive impairment in verbal and working memory, executive function/reasoning and problem solving, compared to depressive, mixed, and euthymic subgroup. Low-neurocognitive performance was directly associated with a predominance of manic episodes and severe course of bipolar illness. An increased number of past manic episodes was the strongest correlated event with the poorest outcomes in verbal memory testing. Other factors correlated with poor verbal memory scores in manic subgroup were age at illness onset (positive correlation), illness length, and hospitalizations (negative correlations).
Bipolar patients showed cognitive deficits regardless of the phase of illness. Subjects experiencing a manic episode displayed higher deficits in verbal and working memory, executive function/reasoning, and problem solving. Severe course of illness also showed significant contribution in terms of cognitive impairment.