Psychiatric disorders in dementia

Alzheimer’s disease (AD) is the most common form of dementia, a neurodegenerative disorder which is characterized not only by cognitive deterioration but also by a diversity of Behavioral and Psychological Signs and Symptoms of Dementia (BPSD). BPSD in AD or other dementia subtypes such as frontotemporal dementia (FTD) or dementia with Lewy bodies (DLB) consist of delusions, hallucinations, activity disturbances, aggression/agitation, diurnal rhythm disturbances, mood disorders, apathy, and anxieties/phobias. Neuroimaging modalities such as positron emission tomography (PET) and single- photon emission computed tomography (SPECT) are very essential and useful imaging tools to differentially diagnose between AD and non-AD or healthy control subjects or between different dementia subtypes, such as AD and DLB or FTD. Besides their diagnostic characteristics, PET and SPECT are also useful tools to investigate the cerebral pathophysiology of BPSD in AD, FTD, and DLB among others. Below, PET- and SPECT-related neuroimaging in dementia spanning the last two decades has been reviewed. The common use of different PET and SPECT radioligands and other compounds which target different and unique aspects of neurodegeneration in the differential diagnosis of dementia is described. Furthermore, PET and SPECT research in BPSD with a main focus on depression, apathy, and psychosis in AD, DLB, and FTD are illustrated as well. On the whole, both PET and SPECT imaging of neuropsychiatric disturbances in dementia have demonstrated that depending on the behavioral phenomenon and dementia subtype, BPSD are the fundamental expression of very regional cerebral pathological events rather than a diffuse brain illness.