The induced psychosis, also known as folie à deux, was first described in 1887 by Lasegue & Falret and is characterised by the transmission of delusional beliefs from a psychotic individual to a healthy individual. The article described the disorder as a syndrome occurring predominantly in women living in sheltered, isolated conditions. The syndrome was characterised by the emergence of the same psychotic symptoms in members of a family while living together, or in two very close individuals, and the transmission of psychotic symptoms from an affected individual to one or more healthy persons.

However, Machado de Assis, the Brazilian author, wrote a fictional story published 8 years before the article by Lasegue & Falret, which contains an accurate description of folie à deux. In his story, Rafael the Angel, Assis narrates the life of a man who believed that he was the angel Rafael himself. This man lived in isolation on a farm with his daughter, who had no contact with the outside world until the age of 15. Shortly before his death her father found her a suitor, who soon realises she had been contaminated by her father's delusions: not only did she believe that he was an angel, but defended this notion despite the disbelief of her new-found fiancé. Following the death of her father she moved from the countryside to the city and 3 months later presented no delusional beliefs.

Assis’ narrative presents a picture which combines all the elements subsequently described by Lasegue & Falret: a woman living in isolation and closely related to a psychotic family member who manifested identical psychotic symptoms and was the influence and the primary cause of her delusion. Assis went further and described the therapeutic effect of separating the individuals.

This story illustrates that, above all, literature can contribute to psychiatry by offering descriptions of conditions in remarkable detail. As noted by Sigmund Freud in Writings on Art and Literature, ‘the poetic treatment of a psychiatric theme can turn out to be correct without any sacrifice of its beauty’, what can be verified in this ‘first case report’ of folie à deux.

Daniel Martins de Barros, Institute of Psychiatry, Geraldo Busatto Filho, Institute and Department of Psychiatry, Medicine School, University of Sao Paulo.