Study results published in the Journal of Affective Disorders describe distinct cognitive subgroups in patients with bipolar disorder, supporting a “continuum of [disease] severity.”
Adult patients with bipolar disorder were recruited by convenience from the Bipolar Disorders Program at a hospital in Southern Brazil (n=73). In addition, a set of healthy controls with no psychiatric history (n=57) were selected for inclusion in the study. Clinical and demographic features were obtained through a structured interview and from medical records. Patients were administered the Hamilton Depression Rating Scale and the Young Mania Rating Scale to assess disorder symptomatology. Overall functioning was assessed according to the Functioning Assessment Short Test, and the Cognitive Complaints in Bipolar Disorder Rating Assessment was used to obtain a subjective measure of cognitive impairment. Finally, patients underwent a battery of neuropsychological tests for objective cognitive measures.
Investigators identified 3 distinct cognitive subgroups in patients with bipolar disorder: intact cognition (43.5%), selective cognitive impairment (33.3%), and global cognitive impairment (23.3%). Discriminant function analysis validated these 3 clusters, with 89.9% of patients correctly classified. Patients with intact cognition were comparable to healthy control participants, whereas patients in the selective group had an intermediate cognitive profile with poorer performance than control participants in all cognitive domains, except for social cognition. Patients in the globally impaired group displayed impairment in all cognitive domains. Compared with the selectively impaired group, participants in the globally impaired group showed poorer performance in verbal memory (P =.023), attention (P =.001), and social cognition (P <.001). The “intact” subgroup had more years of education and a higher estimated intelligence quotient compared with the globally and selectively impaired subgroups (both P <.001). Compared with the globally impaired group, patients with intact cognition were also younger (P =.011) and had a younger age at diagnosis (P <.037) and first hospitalization (P <.035).
These data underscore the existence of a continuum of severity in bipolar disorder. Both subjective cognitive difficulties and functional impairment were observed in the selective and global subgroups. The use of multiple instruments to measure cognition may assist clinicians in obtaining a complete cognitive profile of patients and thus in individualizing treatment.
Lima F, Rabelo-da-Ponte FD, Bücker J, et al. Identifying cognitive subgroups in bipolar disorder: a cluster analysis. J Affect Disord. 2018;246:252-261.