Cognitive scores as a potential diagnostic tool in schizophrenia: The use of raw and discrepancy scores

Abstract

Objective: Cognitive scores could be a useful tool when discriminating between patients with schizophrenia (SZ) and non-psychiatric population. However, whether these scores can contribute to the accurate diagnosis of the disease is still unclear. Therefore, this study aimed to identify the best approach as to the inclusion of cognitive impairment as a potential clinical tool in the diagnosis of SZ. Method: A total of 258 patients with SZ and 202 healthy controls (HC) were assessed by means of the Hopkins Verbal Learning Test-Revised (HVLT-R) and the Trail Making Test-A (TMT-A). In addition to raw scores, participants' discrepancy scores (DS) in these two cognitive measures were calculated using regression-based norms controlling for age, years of education and premorbid intelligence quotient. Receiver-operating characteristic analyses were performed for both scores in order to assess their diagnostic properties. Results: The areas under the curve (AUC) of the HVLT-R total and delayed recall, and TMT-A raw scores were statistically significant and ranged from 0.67 to 0.87. Although significant, AUC of verbal memory DS were lower than those of raw scores (AUC = 0.84; AUC = 0.80). AUC of TMT-A DS was not significant. Conclusions: Results suggest that cognitive scores are useful and accurate when discriminating and classifying patients with SZ and HC in the present sample. Raw scores were shown to be more accurate than DS in patients with SZ and to present good diagnostic properties especially regarding verbal memory measures. Obtained indices support the use of cognitive scores as diagnostic criterion in the diagnosis of SZ.