Some people with dementia are reported to have abnormal beliefs and delusions. Researchers herein examined the prevalence of delusions, and their neurocognitive basis in a large, well-characterized cohort of dementia patients using a transdiagnostic, cross-sectional approach.

• Among 487 people with dementia recruited in this study, there were 102 people with Alzheimer's disease, 136 with behavioral-variant frontotemporal dementia, 154 with primary progressive aphasia, 29 with motor neuron disease, 46 with corticobasal syndrome, 20 with progressive supranuclear palsy.

• Delusions were reported in 48/487 patients (10.8%).

• There appeared an increased risk of delusions in correlation with a diagnosis of behavioral-variant frontotemporal dementia (18.4%) and Alzheimer’s disease (11.8%).

• There were 11/27 people with delusions exhibiting a positive gene mutation.

• Performance on the Addenbrooke’s Cognitive Examination was relatively worse for individuals with frequent delusions, this was particularly evident on the orientation/attention and memory subtests.

• In Voxel-based morphometry analyses, a correlation of increased delusional psychopathology was observed with decreased integrity of the right middle frontal gyrus, right planum temporal and left anterior temporal pole.

• Clinically, delayed or misdiagnosis may occur because of delusions.

• In light of these results, individuals at risk of neuropsychiatric features of dementia could be identified, a crucial first step to enable targeted symptom management.