A – 119 Delusional Paramnesias Differ Across Neurodegenerative Disease Syndromes

Abstract Objective Delusional paramnesias are poorly understood in neurodegenerative syndromes. Thus, we used one consistent method to compare misidentification delusions in a large, well-characterized sample of patients with common neurodegenerative syndromes. Method Participants included 1,515 individuals who underwent comprehensive multidisciplinary diagnosis at a tertiary academic dementia center. They included N=722 with AD and N=315 with behavioral-variant frontotemporal dementia (bvFTD). AD patients were further divided into early-onset (age< 65; EO-AD; n=263), late-onset disease (LO-AD; n=387), and those with clinical evidence of comorbid Lewy-body disease (AD-LBD; n =175). Content of psychotic belief was assessed at the time of first evaluation using the Neuropsychiatric Inventory (NPI). Fisher’s exact tests were run to identify differences in prevalence of psychosis content across neurodegenerative syndromes. Results At least one delusion was reported in 15% of participants (226/1515). Of those with delusions, LO-AD (10/76, 13%) and AD-LBD (7/46, 15%) were significantly more likely than bvFTD (0/45) to experience reduplicative paramnesia (i.e. their home has been replaced) (p< 0.05). Additionally, AD-LBD was 10.48 (odds ratio, p< 0.05) times more likely to cause Capgras delusions (i.e. other person is an imposter) (9/46, 20%) than bvFTD (1/45, 2%). Delusional content did not differ between EO-AD and bvFTD. Conclusion When experiencing a psychotic delusion, individuals with late-onset AD and AD with clinical evidence of comorbid Lewy-body disease are more likely to experience delusional paramnesias of place and person than individuals with bvFTD. Interestingly, no participants with bvFTD endorsed reduplicative paramnesia of their home. This striking heterogeneity of delusion content across syndromes suggests a specific neurobiological etiology for specific psychotic beliefs.