1. Frégoli Syndrome

• Definition: A delusional belief that different people are, in fact, a single individual who changes appearance or is in disguise.
• Example: A person believes that a stranger they encounter is their friend or enemy, disguised to manipulate or stalk them.
• Cause: Often associated with brain lesions, schizophrenia, or traumatic brain injuries.
• Named After: The Italian actor Leopoldo Frégoli, known for his ability to change appearances rapidly on stage.

2. Cotard Syndrome

• Definition: A rare condition where a person believes they are dead, non-existent, or missing body parts.
• Example: A patient may claim, “I don’t have a brain” or “I am dead and don’t need food.”
• Symptoms: May include severe depression, psychosis, and nihilistic delusions.
• Cause: Typically associated with major depressive disorder, psychotic disorders, or neurological diseases like stroke or tumors.
• Named After: Jules Cotard, a French neurologist who first described the condition in 1880.

3. Capgras Syndrome

• Definition: A delusional belief that someone close to the person, such as a family member, friend, or partner, has been replaced by an identical imposter.
• Example: A person may insist that their spouse is not actually their spouse but someone pretending to be them.
• Cause: Linked to brain injuries, schizophrenia, or dementia, particularly Alzheimer’s disease.
• Named After: Joseph Capgras, a French psychiatrist who first described the syndrome in 1923.

Differences:

• Frégoli Syndrome involves multiple people being perceived as one individual.
• Cotard Syndrome involves a belief in non-existence or death.
• Capgras Syndrome involves a belief in imposters replacing familiar people.