A man wakes from a nap, walks up to the woman he has been married to for fifty years, and asks who she is. He can describe her face accurately. He knows what his wife looks like. He is simply unshakably certain that this particular woman is not her.
That is Capgras syndrome, and for a century it has been filed mostly under psychiatry. A retrospective cohort study from the Mayo Clinic, published in the journal Brain, is the greatest effort yet to determine what actually drives it. The answer is not the one the textbooks emphasize.
The Delusion Is Mostly Neurological, Not Psychiatric
Researchers reviewed the records of every patient diagnosed with Capgras syndrome at Mayo Clinic in Rochester, Minnesota, over 28 years, from January 1995 through December 2022. They found 204 of them. The median age at onset was 73, and 44% were women.
Neurodegenerative disease accounted for 69% of cases. Within that group, one condition dominated: dementia with Lewy bodies, at 58% of the total. Mixed causes made up another 18%, and Alzheimer's disease 10%. Primary psychotic disorders, the category most people associate with delusions, accounted for just 9%.
Twelve patients went on to autopsy. All twelve showed alpha-synuclein pathology, the abnormal protein deposits that define Lewy body disease, including one patient who had been diagnosed clinically with Alzheimer's disease during life.
No case was attributed to a single stroke, although 9% involved coexisting cerebrovascular disease alongside Alzheimer's or Lewy body dementia. The direction of the finding is not new. An earlier Mayo review of 47 patients reached a similar conclusion nearly two decades ago. What the larger cohort adds is scale, imaging, and pathology.
Who Gets Misidentified Turns Out to Be a Clue
The most immediately useful finding for clinicians is not about biology. It is about who the impostor is.
In both dementia with Lewy bodies and Alzheimer's disease, the delusion typically targeted a single person, usually a spouse. In psychotic disorders, it tended to involve multiple people, and those people were often not spouses.
That distinction gives a bedside question real diagnostic weight. How many people has the patient identified as impostors, and who are they? A single spouse points in one direction. Several acquaintances point to another.
Timing followed patterns too. In dementia with Lewy bodies, Capgras syndrome generally appeared after cognitive decline and after the core features of the disease, meaning visual hallucinations, fluctuating attention, and parkinsonism. But in patients whose Lewy body disease began with psychiatric symptoms rather than memory loss, the delusion showed up earlier. The authors suggest Capgras syndrome could serve as an early diagnostic clue for a disease that is notoriously hard to catch.
The Delusion Got Worse After Dark
Among the 52 patients for whom the information was recorded, 87% had symptoms that worsened in the evening or at night. Depression or anxiety was documented in 55% of the full cohort.
The researchers read that combination as evidence that emotional state feeds the delusion rather than merely accompanying it. Neuroimaging with MRI and FDG-PET showed widespread involvement across both hemispheres, with prominent dysfunction in the right frontal lobe in both Lewy body dementia and Alzheimer's.
The classic explanation for Capgras syndrome is a disconnection model. Face recognition works, but the emotional response that normally accompanies a familiar face does not, and the mind resolves the mismatch by concluding that the person is a copy. A National Library of Medicine reference summary describes the condition as the most prevalent of the delusional misidentification syndromes and notes that organic disorders account for roughly a quarter to two-fifths of reported cases.
The Mayo data suggest something less tidy than a single broken circuit: a multifactorial process driven by broad cortical dysfunction and shaped by mood, fatigue, and time of day. The evening pattern in particular is hard to square with a purely structural explanation, since a damaged connection does not repair itself at breakfast.
Treatment results were sobering. Among 82 patients with Lewy body dementia or Alzheimer's who received cholinesterase inhibitors, 15% improved. That is 12 out of 82 people.
What This Means for the Person Being Called an Impostor
The practical burden of Capgras syndrome usually falls on the person providing daily care, because that is often the person the patient no longer recognizes.
The consequences are not abstract. A review of 109 published Capgras incidents dating from 1971 to 2017, compared against a group of psychiatric inpatients, found high levels of interpersonal violence, directed particularly at main caregivers. A person who believes their caregiver is a stranger may also refuse medication from that caregiver's hand, which turns a delusion into a treatment problem.
Cleveland Clinic guidance for families notes that Capgras syndrome does not appear to affect voice recognition and suggests saying hello before you come into view. It also advises against trying to prove you are not an impostor and recommends arranging temporary relief by asking someone else to step in as primary caregiver for a period.
Several caveats apply to the study. It is retrospective, drawn from records at a single referral center, which skews toward patients sick enough to reach a major academic hospital. Only 12 of 204 patients had autopsy confirmation. Antipsychotics, the historical default treatment, carry particular danger in Lewy body dementia, where patients can react severely, so nobody should adjust medication based on a research finding.
What the study does establish is a shift in where to look. A new impostor delusion in an older adult is a neurological event far more often than a psychiatric one, and the specific disease behind it is usually the one people have heard of least.
Key Questions Answered
What is Capgras syndrome?
A delusional misidentification syndrome in which a person believes someone familiar has been replaced by an identical-looking impostor. Visual recognition stays intact; the sense of familiarity does not.
What did the Mayo Clinic study find?
Across 204 patients seen over 28 years, 69% had neurodegenerative disease, with dementia with Lewy bodies accounting for 58% of all cases. Psychotic disorders made up 9%.
Why does it matter which disease is behind it?
Because management differs sharply. Antipsychotics carry a particular risk in Lewy body dementia, and identifying the underlying condition changes the entire treatment approach.
Does the pattern of who gets misidentified mean anything?
The study found neurodegenerative cases usually targeted a single spouse, while psychotic cases more often involved multiple, non-spousal targets.
Is there an effective treatment?
Not reliably. Among 82 patients with dementia treated with cholinesterase inhibitors, 15% improved. Treatment targets the underlying disease.
What should a caregiver do if they are the accused impostor?
Speak before you come into view, since voice recognition often survives. Avoid arguing with the belief, arrange breaks from caregiving where possible, and raise the symptom with the treating clinician.
