Meta-analysis of Cognitive Impairment in First-Episode Bipolar Disorder: Comparison With First-Episode Schizophrenia and Healthy Controls.

Neurocognitive deficits are evident both in established schizophrenia and bipolar disorder (BP). However, it has been suggested that schizophrenia, but not BP, is characterized by neurodevelopmental abnormalities that can lead to cognitive deficits at the earliest stages of the illness. The aim of this meta-analytic review was to compare neurocognitive deficits in first-episode BP (FEBP) with healthy controls and first-episode schizophrenia (FES) patients. The current meta-analysis included a total of 22 adult studies and involved comparisons of 533 FEBP patients with 1417 healthy controls and 605 FEBP and 822 FES patients. FEBP patients were significantly impaired in all cognitive domains (d = 0.26-0.80) and individual tasks (d = 0.22-0.66) investigated. FES patients significantly underperformed FEBP patients in most cognitive domains (d = 0.05-0.63) and on individual tasks (d = 0.13-0.77). Neuropsychological impairment, which is comparable to chronic BP, was evident in FEBP. Similar to chronic patients, cognitive functions in FEBP lie intermediate between FES and healthy controls. Neurodevelopmental factors are likely to play a significant role not only in schizophrenia but also in BP.