Décrite pour la postérité par Lasègue et Falret en 1877, l’entité psychiatrique Folie à Deux, dont l’incidence demeure difficilement évaluable (estimée de 1,7 à 2,6 %, Wehmeier et al., 2003) et principalement abordée à l’aune d’études de cas (Arnone et al., 2006), continue de susciter l’intérêt nonobstant une littérature scientifique peu abondante. À l’instar de ces travaux, cet article relate un cas familial de délire à deux à travers le cas d’une patiente, Madame A, depuis son hospitalisation en service de psychiatrie jusqu’à un an après sa sortie. Les différents entretiens menés avec elle, l’exploration de la symptomatologie clinique au moyen de la PANSS (Kay et al., 1987 ; Lancon et al., 1999), les rencontres avec ses parents et l’utilisation d’un questionnaire de personnalité (PDQ-4+ [Hyler, 1994 ; Laconi et al., 2016]) ainsi que les éléments biographiques significatifs sont ainsi décrits, avec tentative d’explicitation des différents biais cognitifs à l’œuvre à la fois chez la patiente et chez ses parents. Cet article propose par ailleurs une lecture interactionnelle à la lumière de la thérapie systémique stratégique brève de Palo-Alto, à travers un questionnement quant aux dynamiques familiales entourant cette patiente et son évolution. Le lecteur familier de thérapie systémique pourra en effet retrouver des concepts essentiels comme le caractère symétrique ou complémentaire d’une relation, les principes de totalité, d’équifinalité, d’homéostasie et de rétroaction propres aux systèmes ouverts.

In a relatively small scientific literature, it appears that the psychiatric entity “Folie à deux”, whose incidence remains difficult to assess (estimated from 1.7 to 2.6%, Wehmeier et al., 2003), is mainly approached in the light of case studies (Arnone et al., 2006). In line with this work, our article relates the case of a 51-year-old patient, Mrs. A, from her hospitalization in psychiatric unit until one year after her release, by retracing the significant elements of her history, with an attempt to explicit the different cognitive biases at work. This article proposes to adopt a systemic interpretative framework, through a questioning of the family dynamics surrounding the patient and her evolution. Upon her admission, the Positive and Negative Syndrome Scale (Kay et al., 1987; Lancon et al., 1999) was used, suggesting a diagnosis of late onset schizophrenia, characterized by a predominance of persecutory themes. Over time, her mood improved with Olanzapine, and her persecutory ideas diminished, although she did not criticize her beliefs. Interviews with Mrs. A. and her parents revealed cognitive biases such as external attributional style among the parents. The patient and her mother displayed also arbitrary inferences, overgeneralization and bias against disconfirmatory evidence. The PDQ-4+ personality questionnaire (Hyler, 1994; Laconi et al., 2016) highlighted paranoiac traits in both parents. Mrs. A. background revealed a social isolation, with elements indicating a possible premorbid schizoid personality; the onset of her delusions coincided with conflicts involving neighbors. She was hospitalized for one month; therapeutic alliance was established, facilitating her follow-up despite the cessation of medication. One year later, she manifests a partial insight into her delusions. Although cognitive biases persisted, she also manifested a less restriction in daily life activities. We propose then a systemic interpretative framework, drawing on principles from the Palo-Alto's school: the family dynamics play a crucial role in the emergence of shared delusions and the relationship between Mrs. A and her mother exhibits characteristics of both symmetry and complementarity. The delusional process may represent an attempt to equalize the power dynamics within their relationship. In conclusion, this article posits that the delusions experienced by Mrs. A and her mother can be understood as an emergent property of their family system. The interplay of their personalities and the dynamics of their relationship contributed to the development and maintenance of “Folie à Deux”. This case underscores the importance of considering systemic factors in the assessment and treatment of this trouble.