Tentative de diagnostic différentiel des psychoses fonctionnelles non affectives au moyen des tests neuropsychologiques dans une population congolaise

Abstract

Objectives Schizophrenia, Schizophreniform Disorder and Brief Psychotic Disorder constitute the main part of non-affective functional psychoses of the forth edition of Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). The DSM-IV primarily recognizes the same symptoms in them; it differentiates them only by the disease duration. It is thus difficult to make the differential diagnosis of the three affections at the beginning of the disease. However, they do not have the same prognosis and Schizophrenia, famous for its poor prognosis, requires energetic and early treatment which requires an early positive diagnosis. Hence the need to lay out tools for differential diagnosis other than symptoms. The authors studied the possibility to make the differential diagnosis of the three affection through neuropsychological assessment. Subjects and methods The sample comprised 70 schizophrenics, 68 patients with Brief Psychotic Disorder and 50 with Schizophreniform Disorder, all Congolese people, recruited in “Centre neuro-psychopathologique” of the university of Kinshasa and the mental health center “Téléma” in Kinshasa, from 5 August 2003 to 14 March 2005. Neuropsychological performances of the three patients groups at a conventional neuropsychological battery for schizophrenics were compared. A principal components analysis provided the cognitive factors used to compare the three patients groups. The comparison based on the one way analysis of variances (ANOVA), Tukey's test and multivariate discriminant analysis, whilst controlling for demographic variables, clinical syndromes and neuroleptics side effects. Results Five cognitive factors were identified: factor 1 with high loadings on tests of frontal functions, nonverbal memory and nonverbal general intelligence, factor 2 with high loadings on tests measuring the time and speed of execution of mental tasks, factor 3 measuring frontal controlled processes, factor 4 measuring verbal memory and factor 5 measuring attention. The multivariate discriminant analysis was conclusive (F = 2.55; df = 2; P = 0.0055). However the overall error count estimate was too high (53%) and no convincing neuropsychological profile specific to each of the three affections could be released. Only verbal memory – not frontal functions nor attention – affirmed some discriminant power. Clinical variables showed more important differences between the patients groups. The founded differences showed that Brief Psychotic Disorder was different from Schizophrenia and Schizophreniform Disorder. The discrimination between Schizophrenia and Schizophreniform Disorder was less obvious; we failed especially to identify patients with Schizophreniform Disorder. Conclusions The used neuropsychological tests could not be used without caution in making differential diagnosis of the studied affections, however the importance of the 15 words of Rey, measuring verbal memory is highlighted. Other types of variables, e.g. the clinical one, could be more recommended to make the differential diagnosis between the three affections.