Classification & Assessment in Psychiatry · Paper A
Delusional misidentification (Capgras and related)
In the delusionalRelating to a fixed false belief held with total conviction despite evidence against it.Read more → misidentification syndromes, a person becomes convinced that the identity of someone, or somewhere, has changed. They occur in schizophreniaA long-term mental illness involving episodes of psychosis such as hallucinations and delusions.Read more → (a chronic psychotic illness) and especially in organic (physical) brain disorders. E.g. a patient insists their spouse has been replaced by an identical impostor, while still recognising the impostor looks identical; this is Capgras syndromeA delusion that a familiar person has been replaced by an identical impostor.Read more →. Clinically, a sudden misidentification belief like this should prompt screening for an organic brain cause, not just a psychiatric one.
Capgras syndromethe belief that a familiar person has been replaced by an identical impostor (one theory is that face recognition is intact but disconnected from the normal feeling of familiarity). Fregoli syndromeA delusion that different people one meets are actually a single person in disguise.Read more →: the belief that a stranger is really a familiar persecutor in disguise. Intermetamorphosis: the belief that people swap both identity and appearance. Syndrome of subjective doubles: the belief that doubles of oneself exist. E.g. a patient believes every stranger is the same persecutor in disguise and tracks them everywhere; that pattern is Fregoli syndrome, not Capgras. In practice, the two syndromes are told apart by whether the misidentified person is familiar (Capgras) or a stranger (Fregoli).
Most delusions (fixed, false beliefs not shared by one's culture, held despite clear contrary evidence) are about content: persecution, guilt, grandeur. Delusional misidentification syndromes are different: they are specifically about identity, the belief that a familiar person, or a familiar place, has somehow been swapped, duplicated, or is not what it appears to be. Grouping them together matters clinically because they share a common association with organic (physical) brain disease, more so than most other delusions, and that changes the required work-up.
A misidentification syndrome is a fixed false belief that the identity of a person, or occasionally a place, has changed in some specific, patterned way. They occur in (a chronic psychotic illness featuring , and disorganised thinking) and, notably, in organic brain disorders such as dementia, stroke or traumatic brain injury, more often than most delusion types.
The single most important fact to hold onto: because organic brain disease features so heavily in these syndromes, any new misidentification , especially in someone older, or with a history of head injury or vascular risk factors, should prompt investigation for an organic cause (brain imaging, cognitive screening), not an automatic assumption of primary psychotic illness. The second common error is confusing the four named syndromes with one another, since exam questions are built specifically around telling them apart.
One influential theory treats face recognition as having two separate steps: first, recognising a face as familiar (a fast, largely automatic visual process), and second, feeling the emotional sense of familiarity that normally accompanies recognising someone you know. is thought to occur when the visual recognition step works, the patient does see that the impostor looks identical, but the emotional-familiarity step is disconnected, so the face is correctly matched yet feels wrong, and the brain resolves that contradiction by concluding the person must be a fake. This "right face, missing feeling" model helps explain why patients can insist someone looks exactly like their spouse while still believing they are not their spouse.
Picture a 68-year-old man with early dementia who tells his daughter that his wife of forty years "looks exactly like her, but she isn't: the real one has been replaced." He recognises every physical detail correctly, but the belief persists regardless. This is Capgras syndrome: a familiar person believed to be an impostor. Contrast this with a patient who insists that a series of different strangers on the ward are all actually the same person (perhaps a persecutor) appearing in disguise each time; that pattern, strangers believed to be one familiar person in disguise, is Fregoli syndrome, essentially the mirror image of Capgras.
Capgras syndrome: a familiar person is believed replaced by an identical impostor. : an unfamiliar person (a stranger) is believed to be a familiar person in disguise. Intermetamorphosis: the belief that people swap both their physical appearance and their identity with one another. Syndrome of subjective doubles: the belief that duplicate versions of oneself exist elsewhere. Reduplicative paramnesia applies the same duplication idea to a place rather than a person: the belief that a familiar location (often the hospital ward itself) has been duplicated and exists in two places at once. These are distinguished from Cotard syndrome (the belief that one is dead, does not exist, or is rotting), ( jealousy: the fixed belief a partner is unfaithful without evidence), and de Clerambault syndrome (erotomania: the belief that another person, often of higher social status, is secretly in love with you).
Diagnosis is clinical, established through psychiatric history-taking and mental state examination that elicits the specific, fixed, false belief and confirms it is held with full conviction despite contrary evidence, per standard ICD-11 and DSM-5 criteria for a within a psychotic disorder. Because organic causes are so relevant here, work-up typically extends beyond the psychiatric interview to include cognitive testing, and brain imaging (CT or MRI) is considered, particularly to look for right-hemisphere lesions, which are classically over-represented in .
Management targets the underlying cause first: if an organic driver (a new stroke, a subdural haematoma, an evolving dementia) is found, that condition is treated directly, following NICE guidance on the relevant underlying disorder (for example NICE guidance on dementia assessment and management). Where the misidentification causes distress or risk (a patient becoming aggressive toward a "replaced" spouse), a low-dose antipsychotic is used symptomatically, alongside reassurance-based approaches and support for family members, who often find these delusions especially distressing since they are being personally disbelieved or replaced in the patient's mind.
If a vignette gives a right-hemisphere brain injury or an elderly patient with cognitive decline alongside an impostor belief, expect the answer to be plus "arrange brain imaging," not simply "start an antipsychotic." If the vignette instead describes the SAME person appearing as multiple different strangers, that is Fregoli, and if a PLACE (not a person) is duplicated, that is reduplicative paramnesia.
misidentification syndromes are fixed beliefs about a changed identity: Capgras (impostor), Fregoli (familiar person in disguise), intermetamorphosis, subjective doubles, or reduplicative paramnesia for a place, and their strong link to organic brain disease means a new case should prompt investigation, not just treatment.