Delusional Misidentification Syndrome

Delusional misidentification syndromes (DMSs) are complex, often multifactorial, neuropsychiatric delusions with a plethora of clinical presentations. These DMSs can coexist, oscillate interchangeably, or exist at different times in an individual's lifetime. As these delusions can coexist at a rate of 29%, a shared mechanism has been postulated. DMSs are often encountered in major neurocognitive disorders such as Alzheimer dementia (15.8%) and Lewy body dementia (16.6%). The 4 core types of DMSs included Capgras syndrome, Frégoli syndrome, intermetamorphosis, and the syndrome of subjective doubles (see Delusional Misidentification Syndromes and Subtypes). Christodoulou further categorized these core DMSs as "hyper" and "hypo" familiarity regarding heightened over- or underidentification. Violence and dangerousness in patients with DMSs and concomitant major neurocognitive disorders are well documented with a significant amount of forensic case reports. A sizable number of patients with a primary psychiatric diagnosis, most notably schizophrenia, with concurrent DMSs, were noted to have a high rate of murder or attempted murders, with approximately half of the violent acts perpetrated with weapons.  Overlap with the forensic population and DMSs, particularly Frégoli syndrome, has been noted in case studies wherein the patient believes the victim is the actual perpetrator. Studies regarding Capgras Syndrome identified risk factors of violence to include male sex, long-standing delusions, a history of aggressive behavior, a diagnosis of schizophrenia, and comorbid substance use. Delusions of persecution, particularly towards the misidentified person, were common.  Moreover, as the literature suggests that perhaps more than 50% of patients with DMSs have a primary diagnosis of schizophrenia, clinicians should maintain awareness of specific health disparities, management, treatment complications, caregiver burden, and risk factors. According to studies, patients diagnosed with schizophrenia may have a 5% to 10% lifetime risk of suicide, significantly higher than the overall population. Some authors in this literary space have suggested the integration of DMSs into the evaluation of schizophrenia. The right parietal lobe and temporal lobe have been implicated in DMSs.