Relationship between diminished expression and cognitive impairment in first-episode schizophrenia: a prospective three-year follow-up study

Background: Diminished expression (DE) is a core sub-domain of negative symptoms construct in schizophrenia. There is limited, yet inconsistent data regarding DE and its associations with cognition, particularly in the early illness course. This study aimed to examine cross-sectional and longitudinal relationships of DE with cognitive functions in first-episode schizophrenia utilizing a prospective design.

Method: Ninety-three Hong Kong Chinese aged 18 to 55 years presenting with first-episode schizophrenia-spectrum disorder were studied. Severity of DE was measured as sum of individual item scores indicative of affect flattening and alogia. Symptom evaluation was conducted at intake, after clinical stabilization of first psychotic episode, at 12, 24 and 36 months. Cognitive functions were evaluated at clinical stabilization, 12, 24 and 36 months.

Results: DE was significantly correlated with various cognitive functions in successive follow-up assessments. Regression analyses adjusting confounding effects of sex, pre-morbid adjustment, duration of untreated psychosis and chlorpromazine equivalents showed that DE was associated with performance on verbal fluency at 12 (p<0.01) and 24 months (p<0.05), visual reproduction at 24 (p<0.05) and 36 months (p<0.01), logical memory at 36 months (p<0.05) and Modified Wisconsin Card Sorting test at 24 (p<0.05) and 36 months (p<0.05). Neither cross-lagged associations between DE and cognition nor significant correlations between changes in these two domains over three years were observed.

Conclusions: DE and cognitive functions were correlated concurrently but no longitudinal associations between these two domains could be demonstrated. Our findings indicated that DE and cognitive impairment represented relatively independent domains of the illness with potentially distinctive therapeutic implications.