Neuropsychological functioning in bipolar disorder and schizophrenia.
BACKGROUND
Some patients with bipolar disorder (BD) demonstrate neuropsychological deficits even when stable. However, it remains unclear whether these differ qualitatively from those seen in schizophrenia (SZ).


METHODS
We compared the nature and severity of cognitive deficits shown by 106 patients with SZ and 66 patients with BD to 316 healthy adults (NC). All participants completed a cognitive battery with 19 individual measures. After adjusting their test performance for age, sex, race, education, and estimated premorbid IQ, we derived regression-based T-scores for each measure and the six cognitive domains.


RESULTS
Both patient groups performed significantly worse than NCs on most (BD) or all (SZ) cognitive tests and domains. The resulting effect sizes ranged from .37 to 1.32 (mean=.97) across tests for SZ patients and from .23 to .87 (mean=.59) for BD patients. The Pearson correlation of these effect sizes was .71 (p<.001).


CONCLUSIONS
Patients with bipolar disorder suffer from cognitive deficits that are milder but qualitatively similar to those of patients with schizophrenia. These findings support the notion that schizophrenia and bipolar disorder show greater phenotypic similarity in terms of the nature than severity of their neuropsychological deficits.
Schretlen
David J
DJ
Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-7218, and Olin Neuropsychiatric Research Center, Hartford Hospital Institute of Living, CT, USA. dschret@jhmi.edu
Cascella
Nicola G
NG
Meyer
Stephen M
SM
Kingery
Lisle R
LR
Testa
S Marc
SM
Munro
Cynthia A
CA
Pulver
Ann E
AE
Rivkin
Paul
P
Rao
Vani A
VA
Diaz-Asper
Catherine M
CM
Dickerson
Faith B
FB
Yolken
Robert H
RH
Pearlson
Godfrey D
GD
D000328:Adult; D001714:Bipolar Disorder / Q000175:diagnosis* / Q000523:psychology; D003072:Cognition Disorders / Q000175:diagnosis* / Q000523:psychology; D003937:Diagnosis, Differential; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests / Q000706:statistics & numerical data*; D010641:Phenotype; D011597:Psychomotor Performance / Q000502:physiology; D012559:Schizophrenia / Q000175:diagnosis*; D012565:Schizophrenic Psychology; D012720:Severity of Illness Index