Folie a Deux1

The term folie à deux has been used in connection with several psychotic situations involving two persons. Generally, it is applied to the so-called induction (contagion, infection) of a second person by a primary mentally sick person living in close proximity. The inductor suffers from paranoid ideas, excitements or depressions which are transmitted to the second person. Those who are induced, that is, are infected by the primary person, are usually blood relations (siblings, or parents and their children); less frequently the second member of a married couple. This circumstance is interpreted by Bleuler2 to 'throw light on the familial disposition to the disease'.

From psycho-analytic investigation a different explanation of the tendency of folie à deux to develop in blood relatives is tenable. Among blood relatives the possibility for early and intense identification of children with parents and with each other is possible and an inevitable habitual psychological process. This especially affects ideal formation and self-appraisal. It is likely that in folie à deux the process of identification plays a rôle far greater than that of mere proximity or constitutional predisposition, a vague concept emphasized by some observers.

It is a matter of frequent observation that when the induced person is removed from the inductor the symptoms in the former disappear. Exception to this result has been noted, which again led Bleuler to comment that the second person sometimes suffers from an independent disease in which only certain manifestations, such as the content of the delusions, are determined through induction. I believe this to be the case far more frequently than it is possible to demonstrate in advanced folie à deux. In the case of neurosis a deux which I present, the preexistent individual neuroses could be thoroughly established; the mutual symptomatology developed only after marriage.

Mention is made in the description of cases of folie à deux by Brill3