Neuroimaging of delusions in Alzheimer's disease.

MEDLINE, Embase and PsycINFO were searched using the keywords "imaging", "neuroimaging", "CT", "MRI", "PET", "SPECT", "Alzheimer's", "dementia", "delusions" and "psychosis" to find studies specifically assessing or reporting on neuroimaging of delusions in Alzheimer's Dementia (AD), separate from hallucinations or psychosis in general in AD. Twenty-five studies were found meeting criteria and are included in this review which reports on structural, regional perfusion, metabolic and receptor binding imaging modalities assessing delusions as a whole, as well as persecutory and misidentification delusional subtypes. The majority of studies implicate right-sided pathology, primarily frontal lobe. Left-frontal predominance and release, secondary to right-sided pathology, may create a hyperinferential state resulting in the formation of delusions. This perturbation and imbalance of normal networks is associated with delusional phenomenology. Temporal lobe structures are also important in misidentification syndromes, which have a different natural history than paranoid delusions. Consistent with the neuropathological and genetic literature, neuroimaging has shown that paranoid versus misidentification delusions are associated with different phenomenology and different neural substrates. Delusional subtype is an important factor in understanding the neurobiological underpinnings of delusions in dementia. We also discuss methodological issues related to neuroimaging of delusions in AD.