Neuropsychological impairment in deficit vs. non-deficit schizophrenia

This study aimed to assess the severity and specificity of cognitive impairments that affect individuals with deficit versus non-deficit schizophrenia. We compared 26 patients with the deficit subtype of schizophrenia (SZ-D) and 79 with non-deficit schizophrenia (SZ-ND) to 316 healthy adults (NC). All study participants completed a battery with 19 individual cognitive 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 derived cognitive domains including attention, psychomotor speed, executive function, verbal fluency, visual memory, and verbal memory. Multivariate analyses of variance revealed significant group effects for every individual measure and domain of cognitive functioning (all ps<0.001). Post hoc comparisons revealed that patients with SZ-D performed significantly worse than NCs in every cognitive domain. They also produced lower scores than the SZ-ND group in every domain, but only the difference for verbal fluency reached statistical significance. The correlations of the effect sizes shown by the SZ-D and SZ-ND patients were of intermediate magnitude for the individual tests (r=0.56, p<0.01) and higher, but not statistically significant for the cognitive domains (r=0.79, p=0.06). Patients with SZ-D demonstrate cognitive deficits that are both common and distinct from those shown by patients with SZ-ND. Their impairment of verbal fluency is consistent with the observation that poverty of speech is a clinically significant feature of patients with SZ-D.