Monothematic delusion
A delusional state focused on a single topic.
A monothematic delusion is a delusional state that concerns only one particular topic, in contrast to multi-thematic or polythematic delusions typically seen in schizophrenia. These disorders can occur within the context of schizophrenia or dementia, or without any other signs of mental illness, often due to organic dysfunction from traumatic brain injury, stroke, or neurological illness. Notably, some individuals with such delusions have no obvious intellectual deficiency and may even recognize their beliefs are bizarre, yet cannot be persuaded otherwise.
Quick Facts
- Specialty
- psychiatry
Facts from the source article.
Types
Monothematic delusions cover a range of specific beliefs. In Capgras delusion, a person thinks a close relative or spouse has been swapped with an exact lookalike impostor. Fregoli delusion is the idea that different people one meets are actually the same individual in disguise. Intermetamorphosis involves the conviction that someone can change into another person, both in appearance and personality. The syndrome of subjective doubles is the belief that a person has a doppelgänger acting independently. Cotard's syndrome includes the belief that one is dead, does not exist, is rotting, or has lost blood or organs; rarely, it can involve delusions of immortality. Mirrored-self misidentification is the belief that one's own reflection is a different person. Reduplicative paramnesia is the belief that a familiar person, place, object, or body part has been copied—for instance, thinking a hospital is a duplicate in another location. Somatoparaphrenia is the belief that a limb or an entire side of the body belongs to someone else. Some of these are sometimes grouped as delusional misidentification syndrome.
Causes
According to current cognitive neuropsychology, monothematic delusions likely arise from two factors. The first is an unusual experience, frequently caused by a neurological issue. The second is a problem with how the brain forms beliefs. In Capgras delusion, for instance, the first factor involves a breakdown in how the brain processes a familiar face, specifically the emotional connection tied to that person. A patient can recognize a loved one’s face, but seeing it fails to trigger the expected feeling. The mind then interprets this as encountering an impostor who only resembles the loved one. The second factor, a defect in belief formation, is not well understood, and the process itself remains unclear. Although the two-factor model is the leading explanation, some alternatives do not require a second factor. Research shows that people prone to delusions tend to jump to conclusions, making them more likely to accept strange experiences as real and form quick judgments. They also display a stronger matching bias, meaning they seek out evidence that confirms their existing beliefs rather than testing those beliefs against challenges. These cognitive biases help explain how such individuals adopt and cling to extreme ideas, but experts disagree on whether this is enough. Some argue that patients need an additional, largely speculative neurological defect in belief formation, which would probably be located in the right hemisphere of the brain.
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