Diminished expression (DE), a core negative symptom in people with schizophrenia, is significantly correlated with an array of cognitive functions, research by a Hong Kong team shows.
Despite this cross-sectional correlation, however, DE and cognitive function followed different longitudinal paths, suggesting that the two measures are relatively independent domains of schizophrenia.
Wing Chung Chang (The University of Hong Kong, China) and team studied 93 people aged 18 to 55 years who presented with a first episode of schizophrenia, schizophreniform disorder, or schizoaffective disorder. All participants were assessed at baseline and during 3 years of follow-up.
The participants’ mean age at baseline was 31.2 years, 45.2% were male, and the median duration of untreated psychosis was 180 days.
At various timepoints during the study, DE – measured as the sum of individual items scores indicative of affect flattening and alogia – significantly correlated with measures of cognitive function, including the logical memory test, the visual reproduction test, the Modified Wisconsin Card Sorting Test, and verbal fluency.
These correlations remained significant in multiple regression analyses.
However, longitudinal changes in DE did not correlate with changes in cognitive function. For instance, DE score at initial presentation and at clinical stabilization did not correlate with cognitive outcomes at 36 months, and baseline cognitive performance failed to correlate with DE score at 36 months.
Also, there was no significant correlation between change in DE and each of the cognitive domains over 3 years, and early change in DE showed no significant correlation with change in cognitive function or with cognitive outcomes at 36 months.
The authors say that their study lends support to the notion of “relative independence” of DE and cognitive impairment in schizophrenia, in which negative symptoms and cognition are “either distinct dimensions with separable but related etiology or independent domains with observed correlations secondary to other illness-related factors.”
They conclude: “Owing to limited data on the relationship between DE and cognitive impairment, more prospective research with longer follow-up duration should be conducted to clarify the longitudinal course of DE and its association with long-term cognitive outcome.”
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