Introduction
Fixed false beliefs; they are based on incorrect (false) inferences about reality external to, or about, oneself and maintained firmly (fixed) despite the presentation of evidence that obviously and incontrovertibly contradicts the belief.
Delusional misidentification syndromes:
Share the theme of doubles (ie, duplication of self, others, or the environment). They are associated with impairments in facial processing and are closely related to and sometimes co-occur with reduplicative paramnesia.
- Delusional hypoidentification (eg, Capgras syndrome)
- Delusional hyperidentification (eg, Frégoli, intermetamorphosis, subjective doubles syndromes)
Differential diagnosis:
- Obsessive-compulsive disorder: A person who remains convinced that his/her obsessions and compulsions are true convictions, should be given the diagnosis of obsessive-compulsive disorder with absent insight.
- Schizophrenia spectrum disorders: Can be differentiated from delusional disorder by the presence of other symptoms of the active phase of schizophrenia.
- Delirium/major neurocognitive disorder: Can mimic delusional disorder but distinguished based on the chronology of symptoms.
- Depression or bipolar disorder: Delusions occur with mood episodes. A delusional disorder is diagnosed only when the span of delusions exceed the total duration of mood symptoms.