Psychiatric eponyms: De Clérambault’s Syndrome


Also know as erotomania, De Clérambault’s syndrome is one in which a delusional belief is held by a patient that another person, usually older and of higher social status, famous, wealthy or in a professional relationship with the patient is deeply in love with them.

Pursuing the object of their affections and repeatedly pestering them by telephone, by letter and with gifts is typical.  Some people suffering from this disorder arrange ‘holidays’ or ‘weddings’ with their supposed lover.

Key features are:

  • The conviction of being loved
  • Supposed lover does nothing to encourage or sustain the belief, usually making clear their lack of interest or concern
  • Words or actions of supposed ‘lover’ are reinterpreted to maintain belief in requited love
  • Belief that supposed relationship will eventually result in a permanent and loving relationship
  • Preoccupations with supposed love form a central part of the subject’s existence.
  • Repeated attempts to approach the supposed lover creating at least embarrassment and distress.

The condition is rare and has various aetiologies; it can surface in association with schizophrenia or affective disorders, or on its own as a single delusional disorder.  It is seen in forensic populations as a result of criminal acts secondary to the delusion and is one of a number of behaviours that may be associated with stalking.

The disorder is named after French psychiatrist Gaëtan Gatian de Clérambault (1872–1934), who published a review paper on the subject (Les Psychoses Passionelles) in 1921.  The syndrome has featured in popular works, perhaps the best well know of which is Ian McEwan’s Enduring Love.  It is thought to have effected John Hinckley, Jr. who shot President Regan in 1981 in an attempt to impress actress Jodie Foster, who he believed wanted a sign of his devotion.



Wikipedia – Erotomania
Who named it?

Updated December 2018

Psychiatric eponyms: Capgras syndrome

invasion of the body snatchers

Capgras syndrome is one in which a patient has a delusional belief that a person or persons, usually well known to them, have been replaced by an identical impostor(s).  It usually occurs in the context of a psychotic illness (more than half of cases are associated with schizophrenia) but may be seen with other psychiatric illnesses, including brain injury or dementia.

The Capgras delusion is one of a number of delusional mis-identification syndromes, a class of delusional beliefs that involves the mis-identification of people, places or objects.

Joseph Capgras (1873-1950) was a French psychiatrist who first described the disorder in a 1923 paper co-authored with Reboul-Lachaux about the case of a French woman who complained that various ‘doubles’ had taken the place of people she knew.  They called this ‘L’illusion des sosies’ (the illusion of doubles).

Current thinking as to the cause of Capgras syndrome has focused on dysfunction of the inferior temporal cortex and the amydala.  The former is involved with recognising faces and the latter with the simultaneous emotional reaction.  These two structures can be damaged independently;  if the ability to recognise faces remains intact but the emotional reaction which makes them familiar is absent, it is hypothesised that the conculsion drawn will be that the person in question is an identical impostor.


Capgras delusion – Wikipedia
Capgras syndrome – Who named it?

Uncommon psychiatric syndromes – Enoch, Enoch and Ball – is an interesting book with chapters on this syndrome and others.  I read it on holiday in Syria, which I think shows true dedication to my cause.


Berson RJ. Capgras’ syndrome. American Journal of Psychiatry. 1983. 140 969-978

Ellis HD, Lewis MB Capgras delusion: A window on face recognition Trends in Cognitive Science 2001 5 149-56


nb: if anyone has a view on whether it’s ‘Capgras’ syndrome’ or ‘Capgras syndrome’ then I’d be pleased to hear it.


Updated December 2018

Schizophrenia – a work in progress?

Up until the end of the 18th century mental disorders were divided into roughly four categories: idiocy (congenital intellectual impairment), dementia (acquired intellectual impairment), mania (insanity associated with many delusions and disturbed behaviour), and melancholia (insanity associated with circumscribed delusions and social withdrawal).

Morel in France was one of the first people to put forward the view that that mental disorders could in fact be further separated and classified.  In 1852 he gave the name démence précoce to describe a disorder which he described as starting in adolescence and leading first to a withdrawal, odd mannerisms, self-neglect and eventually to intellectual deterioration.

Kraepelin working in the late nineteenth century took inspiration from general paralysis of the insane – a disease with unity of cause, course and outcome – and argued that there were a discrete and discoverable number of psychiatric disorders.  He sought to distinguish between ‘dementia praecox’ and affective psychosis.  Dementia praecox described patients with a global disruption of perceptual and cognitive processes (dementia) together with early onset (praecox).  Affective psychosis contrasted with relatively intact thinking, later onset and episodic nature of the illness.

It was Bleuler who first used the phrase ‘schizophrenia’.  It is commonly thought that this means ‘split personality’ but Bleuler actually meant the name to reflect the ‘loosening of the associations’; he thought this the essence of the disease.  He described four fundamental symptoms which he deemed essential for the diagnosis:  loosened associations (between different functions of the mind, so that thoughts become disconnected and co-ordination between emotional and volitional processes become weaker), ambivalence (the presence of conflicting emotions and desires), incongruous affect (e.g. vacuous giggling on hearing sad news), and autism (active withdrawal from reality in order to live in an inner world of fantasy)
Unlike Kraeplin, Bleuler felt that affective psychosis and schizophrenia were not strictly delineated but on lay on a continuum.  He also demoted hallucinations and delusions, which to Kraeplin were central, to ‘secondary symptoms’.

More recently, working in the 1950s, Kurt Schneider’s work was fundamentally pragmatic.  He lent on the earlier work of Karl Jaspers – a philosopher psychiatrist who had concentrated on the phenomenology of mental disorders, in particular the un-understandability of psychotic delusions – and aimed to identify characteristics that were peculiar to schizophrenia and which would therefore provide the best guide to the practising clinician.  He identified eleven first rank symptoms of the disorder, all of which were forms of hallucination, delusion or passivity experience.

We can see from the above brief summary of the evolution of schizophrenia as an idea that what is central to the diagnosis has significantly altered as it has passed through the hands of these thinkers.  For Kraepelin the crucial features were intellectual, for Bleuler cognitive and emotional, whereas Schneider pinpointed hallucinations and delusions.  Their ideas are still important as DSM IV/ICD-10 criteria for schizophrenia are a patchwork of the ideas of all three.  Therefore although operationalized criteria have improved the reliability of the schizophrenia diagnosis and outside psychiatry it is considered to be a crystallized entity, not only does there still remain no firm aetiology or diagnostic test for schizophrenia but its very character is still up for question.

Half ton Son

(Although I’ve written this to be read without seeing the programme, it will inevitably be more interesting if you watch it as well. On Channel 4 | YouTube)

In ‘Half ton son’, a delicately titled television program shown on Channel 4 last Sunday night, 19-year-old Billy Robbins from Texas can’t move from his room because he weighs 60 stone. The programme follows him as he struggles into the ambulance that takes him to hospital, as the surgeons remove from him five stone of abdominal fat and then band his stomach, and then as he is eventually separated from his mother in recognition he is unlikely to continue to recover in her presence. How could such a thing happen?

In the film Billy and his mother are clearly ‘enmeshed’. Enmeshed families have members’ whose relationships are unusually tight and at their most extreme they are described as being able to read each other’s minds. Billy’s mother describes herself as Billy’s best friend, and she calls him her ‘baby’. Billy really still is her baby; his weight causes him so much disability that she not only feeds him (8000 calories a day), but also wipes his bottom. We don’t have to be psychoanalysts to see the roots of this; Billy’s older brother died before he was born, and in response she wishes to give Billy everything he needs, and that which she can no longer give her first born, whilst Billy – in his gluttony – seeks in vain to replace his dead brother.

Hand in hand with this enmeshment, the ‘boundaries’ between Billy and his mother are a mess. These boundaries are theoretical constructs that separate an individual from his or her surroundings. Our society is full of them and large part of growing up is learning where they lie. An example would be the inappropriateness, around here at any rate, of French kissing your mother-in-law. Boundaries within a family are of great interest to structural family therapists especially and can be thought of as rigid (leading to disagreement), clear (leading to autonomy) or permeable (a.k.a. fluid or undifferentiated) preventing family members from becoming autonomous.

Billy weight is clearly difficult problem to fix. And fascinating was the reaction of the healthcare professionals. Instead of tackling the root of the problem, the relationship between Billy and his mother, they preferred to tinker around the edge with a technological fix, an extremely risky stomach banding operation. And it’s of note that medical teams are involved at all; here then a demonstration of two cultural forces described by Ivan Illich in his book Medical Nemesis: social and cultural iatrogenesis. Social iatrogenesis is the medicalisation of life, and cultural iatrogenesis, the erosion of traditional ways of dealing with what have now come to be defined as medical problems*.

But, I was thinking on my cycle home today, what of this? What must it be like to be the ‘world’s heaviest teenager’ every day slowly eating yourself to death? Or his mother complicit in her son’s condition, driven by psychological impulses she only partially understands?

*Note that I described Billy’s weight as a problem to ‘fix’ as if he were a machine – these idioms are so ingrained that they are hard to avoid.

Depression, religion and the atheist bus.

Over £50 000 has been raised for an advertisement campaign on London buses intended to spread the word of unbelievers. The slogan, ‘There’s probably no God, now stop worrying and enjoy your life’, whist not being particularly catchy, is interesting.

In dissecting it, there’s a connection implied between religion and anxiety, a plea made to end introspection concerning speculation of the existence of a supreme being – as if this enquiry was somehow reprehensible – and an implication made that religion is the root of all our problems, as if the only thing standing between mortals and earthly contentment is religious belief.

This small campaign, whether your agree with it or not, or whether like me you consider it only marginally less prescriptive than the religious advertisements it seeks to combat, at least feels like a levelling. The campaign, funded mostly by small contributions, represents a rare right to reply. As during so much of our day, we are assaulted with large advertisements, and beyond graffiti, there is scant ability to register our dissent or disapproval.

But what part does a religion belief play in mental well-being?

The best insight I’ve found on this is a 1999 literature review of 80 studies concerning the association of depression and religion. This suggests that people who are involved frequently in organized religion and who highly value their religious faith for ‘intrinsic reasons’ are at substantially reduced risk of depressive disorder and depressive symptoms. They also appear to recover more quickly from depressive episodes and are less likely to become depressed over time. On the other hand the authors say that people who are involved in religion for reasons of ‘self-interest’ are at a higher risk for depressive symptoms.

Two groups – Jews and people who are not affiliated with a religion – are at an elevated risk of depression and depressive symptoms and the authors speculate that these effects are ‘a result of trade-offs in how latent predispositions for psychopathology are expressed in certain religious cultures’.*

Private religious activity and particular religious beliefs, which probably equates to people saying that they are ‘spiritual but not religious’ (we’ve all met them), appear to bear no reliable relationship with depression.

The review states that these associations are modest, but consistent, and does flag up weaknesses in the evidence base. In terms of validity it concerns me that the difference between religious believers who have intrinsic and extrinsic beliefs and their relative vulnerabilities may essentially be a proxy for the personality types amassing under these banners.

* I’ve thought about this last sentence and I’m not entirely sure what it means. Can you help?


The origin of the campaign:

Comment is free: Atheists- gimme five

All aboard the atheist bus campaign

Donate to the campaign: Just giving


Religion and depression, a review of literature

Religion and spirituality, linkages to physical health

Religious involvement and depressive symptoms in primary care elders.

Religion, spirituality and medicine: Psychiatrists’ and other physicians’ differing observations, interpretations and clinical approaches

Related Books:

No Logo – Naomi Klein
Essential reading on corporate intrusion via branding

The God Delusion – Richard Dawkins God is Not Great – Christopher Hitchens
Current atheist calls to arms

What is schizophrenia?

“What is Schizophrenia?”

Someone asked me this at a party recently. It’s a difficult question to answer in a single sentence.

For a start, schizophrenia is not a single disorder. According to the ICD-10 it is a group of disorders, classified under F20 in a chapter called ‘Schizophrenia, schizotypal and delusional disorders’.

F20 is split into the following sub-classifications:

F20.0 Paranoid schizophrenia

F20.1 Hebephrenic schizophrenic schizophrenia

F20.2 Catatonic schizophrenic schizophrenia

F20.3 Undifferentiated schizophrenia

F20.4 Post-schizophrenia depression

F20.5 Residual schizophrenia

F20.6 Simple schizophrenia

F20.8 Other schizophrenia

F20.9 Schizophrenia, unspecified

(I can’t immediately find out what happened to F20.7 – maybe it suffered the same fate as floor number 13 in New York skyscrapers)

The aetiology of schizophrenia is unknown; as this is the case we are forced to define schizophrenia on the basis of a number of symptoms which appear together sufficiently frequently to merit a grouping. In this way schizophrenia is a syndrome rather than a disease. A disease is a disorder with a specific cause and recognizable signs and symptoms whereas a syndrome is combination of signs and/or symptoms that form a distinct clinical picture. The ICD-10 classification system deliberately avoids including aetiology in its definition.

Schizophrenia is a disorder which covers a wide range of cognitive, emotional and behavioural disturbances; there is disintegration in the process of thinking, of contact with reality and a pattern of emotional unresponsiveness.

ICD-10 puts it nicely:

The schizophrenia disorders are characterized in general by fundamental and characteristic distortions of thinking and perception and by inappropriate or blunted affect.

There is no one sign that ‘guarantees’ a diagnosis of schizophrenia. For instance many of the characteristic symptoms of schizophrenia can occur during a manic phase of bipolar disorder or during psychotic depression. However the following ‘fundamental and characteristic disorders of thinking and perception’ are considered to have special importance in the diagnosis of schizophrenia. They are based on Schneider’s first rank symptoms, proposed in 1959 and are:

a) thought echo, thought insertion or withdrawal, and thought broadcasting;

(b) delusions of control, influence, or passivity, clearly referred to body or limb movements or specific thoughts, actions, or sensations; delusional perception;

(c) hallucinatory voices giving a running commentary on the patient’s behaviour, or discussing the patient among themselves, or other types of hallucinatory voices coming from some part of the body;

(d) persistent delusions of other kinds that are culturally inappropriate and completely impossible, such as religious or political identity, or superhuman powers and abilities (e.g. being able to control the weather, or being in communication with aliens from another world);

(e) persistent hallucinations in any modality, when accompanied either by fleeting or half-formed delusions without clear affective content, or by persistent over-valued ideas, or when occurring every day for weeks or months on end;

(f) breaks or interpolations in the train of thought, resulting in incoherence or irrelevant speech, or neologisms;

(g) catatonic behaviour, such as excitement, posturing, or waxy flexibility, negativism, mutism, and stupor;

(h) “negative” symptoms such as marked apathy, paucity of speech, and blunting or incongruity of emotional responses, usually resulting in social withdrawal and lowering of social performance; it must be clear that these are not due to depression or to neuroleptic medication;

(i) a significant and consistent change in the overall quality of some aspects of personal behaviour, manifest as loss of interest, aimlessness, idleness, a self-absorbed attitude, and social withdrawal.

(Source of (a)-(i) ICD-10)

The final thing to say is that the conception of schizophrenia is to a certain extent historical and many textbooks choose to explain schizophrenia as a disorder with reference to the history of its classification. The term itself was Bleuler introduced the term in his 1911 book ‘Dementia praecox or the group of schizophrenias’

More reading material: Beating stress, anxiety and depression

theguardian online today has a story on its main page which is titled ‘Why smiles are better than Prozac’

On closer inspection, it’s less an article, more an advertorial for a book called ‘Beating stress, anxiety and depression’ by Jane Plant and Janet Stephenson.  The  article says that the book is ‘new’ but the page says that it came out at the beginning of May this year.  I can only imagine that they were short of copy and rehashed a press release that they found knocking around the office.

Be this as it may, this is the sort of thing that catches my eye.  The introduction is available for perusal online, and Plant and Stephenson say some sensible things – like advising us to ignore celebrity culture – but I am concerned about some of the things they say particularly when they assert that levels of neurotransmitters should be assessed in patients suffering from depression.  The neurotransmitter hypothesis is problematic, as discussed by and, and this sort of test are likely to be more expensive than meaningful.

Daily Mail article on the same book title: ‘How the wrong drugs could be causing your depression’.

Best read it before I comment further.  If anyone has read it and would like leave a comment below I would be most grateful.

Also in the paper today Rachel Cooke has this to say about reality TV and meeting Jodie Marsh

What strikes you most about Marsh when you meet her is not her pleasure at the unexpected turn her life has taken, but her implacable anger…..(about four paragraphs)….I’ve lost count of the number of times youth workers and criminologists alike have made the connection, as they discuss knife crime, between low self-esteem and anger. Well, there is an awful lot of anger among those who participate in reality TV, the majority of which, it seems to me, is the result of low self-esteem, and Marsh is no exception.

Long term outcome in BPAD and Schizophrenia

Catherine commented:

‘I disagree with the comment about bipolar and schizophrenia being chronic, remitting etc. There are a minority who are so badly affected that they never live independently, but the majority go on to either recover, or manage their illness very well, working, hobbies etc and have a good quality of life.’

The point I was making about the chronicity of schizophrenia/bipolar disorders is that in the film ‘Ruth’ is presented to us has having recovered from her mental health crisis with no mention of follow up.  For anyone who doesn’t know, it’s often common practice in healthcare for a patient to be seen by a doctor on at least a short term basis after a problem has resolved as there may be a chance of it coming back, and psychiatry is no exception to this. We know from the film that she already has a diagnosis of BPAD and so she must have had trouble before.  The episode presented to us is quite severe, so I would say that her chance of having another relapse is high, especially with bipolar disease

Schizophrenia is considered to have a wide variety in outcomes, that said, there are not millions of long term studies; here are the ones mentioned in the Shorter Oxford Textbook of Psychiatry:

Kraeplin Dementia praecox and paraphrenia 1919
Concluded that only 17% of his patients were socially well adjusted many years later

Mayer-Gross Die Schizophrenie in Bumke’s Handbuch der Geisteskrankheiten Vol 9 Springer Berlin 1932
Reported social recovery in 30% patients at 16 years all from the same clinic

Brown et al (1966) reported social recovery in 56% in Schizophrenia and social care Maudsley Monography 17 Oxford University Press  London

Manfred Bleuler (1972,1974) followed up 208 patients who had been admitted into hospital in Switzerland between 1942 and 1943.  Twenty years after admission 20% had complete remission of symptoms and 24% were severely disturbed. 

Ciompi did a larger study looking at 1642 records diagnosed as having schizophrenia between 1900 and 1962, with an average follow up of 37 years.  A third of patient were found to have good or fair social outcome.  Symptoms were often less severe in later life. 

Johnstone E.C. (1991) Disabilities and Circumstances in Schizophrenic patients: A follow up study British Journal of Psychiatry  159 supplement 13 5-46, did a 3-13 year follow up of patients with schizophrenia discharged from 1975 – 1985 and found that almost half had a good social outcome. 

Tsoi and Wong (1991) A fifteen year follow up of Chinese Schizophrenic patients Acta Psychiatrica Scandinavica 84 217-220  did a 15 year follow up of 330 patients with first admission Schizophrenia and in this found that almost one third recovered but 17% remained unable to function outside the hospital. 

Finally in the USA Carone et al (1991 – a busy year) found that only 15% of patients meeting DSM-III criteria for schizophrenia recovered after 5 years. 

Full admission: I haven’t read any of these papers/books, and for these papers to be comparable then they should all use similar definitions for schizophrenia and select similar patients – there would be no utility is comparing patients after their first admission and patients who have been admitted countless times.  With these caveats, it appears that prognosis has improved since schizophrenia was first studied.  In the earlier studies the patients would have had no access to modern pharmaceutical treatments 

Schizophrenia outcome is further discussed in  Schizophrenia Research Volume 1, Issue 6, November-December 1988, Pages 373-384

The factors associated with good prognosis in Schizophrenia:

Sudden onset; Short episode;No previous psychiatric history; Prominent affective symptoms; Paranoid type of illness; Older age of onset; Married; No personality disorder; Employed; Good social support; Good compliance with treatment

Poor prognosis is associated with:

Insidious onset; Long episode;Previous psychiatric history; Negative symptoms; Enlarged lateral ventricles; Male gender; Younger age of onset; Single/separated/widowed/divorced; Personality disorder; Poor work record; Social isolation; Poor complicance with treatment

If you’ve still got the strength, read on for outcome of bipolar affective disorder.  Again this is from the Shorter Oxford Textbook of Psychiatry:

The average length of a manic episode (treated or untreated) is six months

At least 90% of patients with mania experience further episodes of mood disturbance

Over a 25 year follow up on average bipolar patients experience 10 further episodes of mood disturbance

The interval between episodes becomes progressively shorter with both age and the number of episodes

Nearly all bipolar patients recover from acute episodes, but less than 20% of patients with this disorder achieve a period of 5 years of clinical stability with good social and occupational peformance

It is estimated that 10% of patient with unipolar depression will eventually turn out to have a bipolar illness.   

So, with both bipolar affective disorder and schizophrenia, I do think that if a patient has one episode they are likely to be troubled by the illness at a later date and this is what I meant by a chronic condition.       

Physical illness that cause psychiatric disease


Frontier Psychiatrist is sick today, and has been off work.  Ordinarily I might enjoy a day in front of the television working through a box set of Prison Break but I’ve been feeling really low all day.  I knew things weren’t right when I got up this morning and and simply stared at my toast rather than eating it. 

But what better time to examine physical illnesses (‘organic causes’) that cause psychiatric symptoms?

Psychiatry and physical medicine have a complicated relationship.  Psychiatric and physical disease can occur at the same time by chance or physical disease can cause psychiatric symptoms and vice versa. Psychiatric medications also have a large number of side effects.  

Whenever a patient comes into the hospital with psychiatric problems, a full ‘work-up’ should include looking for a physical cause for the problem.  Psychiatrists were a bit rubbish at doing this, but are getting better; the hospital where I work audits whether patients admitted have a physical examination whilst they are on the ward. Patients usually get blood tests and often a CT scan, especially if the presentation is atypical.

Depression has a lot of organic causes: cancer, infection, neurological disorders including dementia, diabetes, thyroid disease, Addisons disease, and systemic lupus erythematosis.  Just having one of these diseases in themselves may be a cause for depression as they can result in substantial disability.  Psychiatry blogger Lake Cocytus tells a tale of delayed diagnosis of metastatic breast cancer due to confusion with depression. 

Anxiety also has a number of organic causes: hyperthyroidism, hyperventilation, phaeochromocytoma, neurological disorders and drug withdrawal. 

Finally, psychosis may also be triggered by an organic cause and these include neurological conditions (e.g. epilepsy and strokes), metabolic conditions (e.g. porphyria), endocrine conditions (e.g. hyper- or hypothyroidism), renal failure, electrolyte imbalance (especially calcium), or autoimmune disorders.

Misidentification Syndromes


Misidentification syndromes are some of the most fascinating psychiatric disorders around.  I would say ‘cool’ but I’m sure that suffering from one can be very dispiriting, and will continue to use this adjective for trainers and indie bands only.  They involve a disturbance in the judgement of uniqueness of certain events.

First up, there’s Capgras Syndrome; also known as I’illusion de sosies (Illusion of doubles).  Here, a person is under the impression that someone close to them has been removed and replaced by an identical looking impostor.  It is named after Joseph Capgras, a French psychiatrist, who described this in a paper published in 1923.

Capgras Syndrome is associated with schizophrenia in more than half the cases. The theory behind it runs like this: when the eye sees a face, the brain processes the information in two parallel streams, which can be damaged independently.  Faces are at once explicitly identified via the temporal cortex and also more rapidly though the amygdala, which is involved with the limbic – emotional processing – system.  We can see an example of this rapid processing if we were to find ourselves running away from something without fully understanding what it is. 

If the temporal cortex path is damaged, the brain will have difficulty in recognising a face.  However, via extra-visual clues, emotional responses to familiar faces are preserved.  Therefore someone with prosopagnosia (inability to recognise faces) will still have an emotional response to the faces of people they know.  If the amygdala path is compromised then the person will still recognise the face, but the expected emotional response will be absent.  This could lead the feeling that a familiar face is ‘not quite right’ and to the erroneous conclusion that his is because of an impostor.

Subtly different is Fregoli Syndrome.  Rather than named after a pioneering psychiatrist, this disorder was named after Leopold Fregoli (1867-1936) who was an Italian actor and the greatest quick change artist of this day.  He was famous for his ability in impersonations and his quickness in exchanging roles, so much so that at times rumours spread that his act was in fact performed by more than one person.  This is also known as the illusion of a negative double, and the suffer believes that various people he or she meets is actually the same person in disguise.  This often has a paranoid flavour, with the sufferer believing that that are pursued by a someone that assumes different identities. 

A sort of combination of Capgras Syndrome and Fregoli syndrome is intermetamorphosis syndrome, first described by P Courbon and J. Tusques (1932); in this, the subject develops the delusional conviction that various people have been transformed physically and psychologically into other people.  This disorder involves false physical resemblance and false recognition. 

Almost there.  Reduplicative paramnesia was described by Pick in 1903 and is often seen in post traumatic brain injuries. With this, there is a belief that a familiar person, place, object or body part has been duplicated. For example, a person may believe that they are in fact not in the hospital to which they were admitted, but an identical-looking hospital in a different part of the country. 

Finally, there’s delusion of subjective doubles, in which a person believes there is a doppleganger or double accompanying the self.  Apparently meetings with doubles were a popular theme of 19th century romantic literature (see Dostoyevsky’s The Double).  It was believed that we each have a doppleganger who normally remains unseen; if we see our doppelganger then death is imminent…