How specific are negative symptoms and cognitive impairment in schizophrenia? An analysis of PANSS and SCoRS

Introduction. Interview-based scales can be used as coprimary measures to complement the assessment of cognitive impairment in schizophrenia. One major question that arises from the use of such tools is how specific they are in relation to other psychopathological domains. We analyse the specificity of the Positive and Negative Syndrome Scale (PANSS) negative subscale and the Schizophrenia Cognition Rating Scale (SCoRS). Methods. We performed a principal component analysis (PCA) of PANSS negative subscale, rated by the interviewer, and SCoRS ratings from three different sources (patient, informant, and interviewer) in 101 patients with schizophrenia. Additionally, we correlated mean SCoRS ratings to PANSS negative subscale items to determine whether any PANSS item is particularly related to cognition. Results. The PCA showed that the two first components, which explained approximately 40% of the total variance of the scales, represent the SCoRS ratings and the PANSS negative subscale ratings, respectively. The mean interviewer SCoRS was significantly correlated with the PANSS negative Item 5 (difficulty in abstract thinking) and with the mean PANSS negative subscale. The latter correlation was no longer significant when "difficulty in abstract thinking" was eliminated from PANSS negative subscale. Conclusions. In general, SCoRS and PANSS negative subscale scores address different constructs; however, the PANSS negative item "difficulty in abstract thinking" seems to address a cognitive dimension.