Behavioral and psychological symptoms in neurodegenerative dementias: harbinger, follower, or constant collateral?

Neurodegenerative dementias such as the behavioral variant of frontotemporal dementia, Alzheimer's disease, and Parkinson's disease dementia are linked to various behavioral and psychological abnormalities. Whether these abnormalities precede, coincide or follow the onset of cognitive symptoms is still controversial in existing literature, with trajectories available so far dependent on types of dementia. The authors aim to review the different kinds of premorbid behavioral symptoms/personality traits associated with an increased risk of developing specific types of neurodegenerative dementia. Neuroticism has been associated with an increased risk of Alzheimer's disease and late-onset behavioral abnormalities with the behavioral variant of frontotemporal dementia. The presence of obsessive-compulsive spectrum disorders in Parkinson's disease dementia is also not rare. Analyzing this evidence, we propose "behavioral biomarkers" as neuroticism in Alzheimer's disease, late-onset behavioral abnormalities in behavioral variant of frontotemporal dementia, and obsessive-compulsive traits in Parkinson's disease dementia. These noninvasive behavioral biomarkers will be of immense help, particularly in developing countries, and will prevent the need for costlier investigations and aid in therapeutic strategies.