[Delusions of negation: 4 case reports].

After explaining Cotard's syndrome and its different developments from 1880 to 1992 by recelling the relations of nihilistic delusions with melancholia and pointing out the topicality of the research (more particularly in the last ten years), we'll give an account of four clinical cases: two cases involving two women aged 69 and 82, undergoing a plain melancholic episode; a case of post-melancholia paraphrenia, and a case of systemized nihilistic delusions during a post-partum melancholia. In the four cases, recovery was achieved thanks to electroconvulsive therapy. The third stage of this work considers the phenomenological and descriptive, as well as physiological and psychoanalytical assumptions adopted by the authors. Lastly, a psychopathological explanation is suggested both from a nosographical point of view, in which nihilism is both a mechanism and a delirious theme, and from a "modelization" point of view distinguishing two stages in Cotard's syndrome: nihilism, and delirious reconstruction strictly speaking. Here will use the concept of negative hallucination which we think underlies this delirium, and from this idea, we'll eventually try to demonstrate how relevant the Freudian theory is in this field.