Last month’s BBC documentary ‘Madness in the fast lane‘ has just come to my attention. It tells the story of Ursula and Sabina Eriksson, two Swedish twins, who were captured on camera as they ran into the traffic on the M6 – apparently without motivation. One spent months in hospital, whilst the other was released from police custody and subsequent events lead to a murder trial.
Unfortunate title aside, the twin’s behaviour appears to have been the result of an episode of folie à deux so is of interest to students of mental disorder.
The documentary is available on YouTube – you’ve got to sign in
Folie à deux
Shared delusional disorder was first described in 1860 by Jules Baillarger, who called the syndrome folie à communiqué. It was later described by Charles Lasègue and Jules Falret, who coined ‘folie à deux’ in 1877. Other names, including shared psychotic disorder, shared delusional disorder, and induced psychotic disorder, have also been suggested.
In folie à deux, one individual develops a delusional belief in the context of a close relationship with another person who already has an established delusional idea. The key features of the disorder are the unquestioning acceptance of the other individual’s delusional beliefs and the temporal sequence of development of the disorder, with one of the individuals having an earlier onset. Although shared psychotic disorder usually involves two individuals, it may involve more than two individuals, including entire family units. The delusion resolves in the second person on separation.
Acute polymorphic psychotic disorder
This is a diagnostic category from ICD-10 and is found under the category of ‘Acute and transient psychotic disorder’ (F23). It is further subdivided into acute polymorphic psychotic disorder without symptoms of schizophrenia (F23.0) and acute polymorphic psychotic disorder with symptoms of schizophrenia (F23.1).
Acute psychotic disorders are characterized by one or a combination of acute onset of delusions, hallucinations or incomprehensible or incoherent speech. Acute polymorphic psychotic disorder is a variant where symptoms change rapidly in both type and intensity from day to day or within the same day. The episode remits completely with no residual symptoms and are not due to substance use.
The diagnostic guidelines are influenced by several historical syndromes including bouffée délirante (literally a ‘puff of madness’). The syndrome was introduced by Valentin Magnan (1835–1916) and Paul-Maurice Legrain (1860–1939) in 1895 as caused by ‘degeneration’, a 19th-century view that attributed mental illness to the spread of modern civilization and urban life.