A neuropsychological study on Leonhard's nosological system

Phenotype validation of endogenous psychosis is a problem that remains to be solved. This study investigated the neuropsychological performance of endogenous psychosis subtypes according to Wernicke–Kleist–Leonhard’s classification system (WKL). The participants included consecutive admissions of patients with schizophrenia spectrum disorder or mood disorder with psychotic symptoms (N = 98) and healthy comparison subjects (N = 50). The patients were assessed by means of semi-structured interviews and diagnosed through the WKL system into three groups: a manic-depressive illness and cycloid psychosis group (MDC), unsystematic schizophrenia (USch) and systematic schizophrenia (SSch). All the participants completed a comprehensive neuropsychological battery. The three Leonhard’s psychosis subtypes showed a common neuropsychological profile with differences in the severity of impairment relative to healthy controls. MDC patients showed better performance on premorbid intelligence, verbal memory and global cognitive index than USch and SSch patients, and they showed better performance on processing speed, and working memory than SSch patients. USch patients outperformed SSch patients in verbal memory, working memory and global cognitive index. Neuropsychological performance showed a modest accuracy for classification into the WKL nosology. Our results suggest the existence of a common profile of cognitive impairment cutting across WKL subtypes of endogenous psychosis but with significant differences on a severity continuum. In addition, classification accuracy in the three WKL subtypes by means of neuropsychological performance was modest, ranging between 40 and 64% of correctly classified patients.