Neuropsychological performance in patients with Soft Bipolar Spectrum during a major depressive episode

Abstract

Background: A growing body of evidence shows that mood disorders form a continuum that is quite large ranging from cyclothymia to bipolar I disorder. Within this continuum a substantial percentages of patients with hypomanic subsyndrome, who do not meet the DSM-IV criteria for bipolar disorders due to its strict requirements on the number of hypo/main symptoms and duration of symptoms, are excluded from DSM diagnostic system and tend to be misdiagnosed as unipolar disorder. One approach to identifying such a huge group of patients is to redefine them as soft bipolar disorder (SBP). Few neuropsychological studies have delineated neuropsychological performance in SBP, compared cognitive deficits in SBP and in other mood disorders such as unipolar disorder (UP) and bipolar II disorder (BPII).

Aims: To determine whether, or to what extent, cognitive deficits of SBP differ from that of UP and BPII.

Methods: Patients with DSM-IV defined major depressive episode (MDE) were subdivided into UP (n=221), BPII (n=138), as well as SBP (n=81) based on the definition of SBP by Akiskal, HS (Psychiatr. Clin. North Am. 22, 517-535). SBP comprised of bipolar II1/2 (cyclothymic depression), bipolar III (antidepressant-associated mania), and bipolar IV (hyperthymic depression). All the patients and 200 healthy controls underwent neuropsychological assessment.

Results: SBP was clinically validated by comparing validators (earlier age of onset, family history of bipolar disorder, recurrent depressive episodes, and past hypomanic symptoms) in SBP, UP, and BPII. Patients with SBP performed significantly better than did patients with UP in the domains of processing speed, verbal working memory, and visual spatial memory. None of the seven cognitive domains tested (processing speed, attention, set shifting, planning, verbal fluency, verbal working memory, and visual spatial memory) differed in SBP and BPII.

Conclusions: Our data suggest that SBP presents bipolar diathesis not only in external validators and hypomanic symptoms, but also in neuropsychological performance. We suggest a necessity of differentiating SBP from UP in order to improve sample homogeneity when studying cognitive deficits in these disorders.