Behavioral disorders in dementia with Lewy bodies: old and new knowledge.

Dementia with Lewy bodies (DLB), the second most common primary degenerative neurocognitive disorder after Alzheimer disease, is frequently preceded by REM sleep behavior disorders (RBD) and other behavioral symptoms, like anxiety, irritability, agitation or apathy, as well as visual hallucinations and delusions, most of which occurring in 40-60% of DLB patients. Other frequent behavioral symptoms like attention deficits contribute to cognitive impairment, while attention-deficit/hyperactivity disorder (ADHD) is a risk factor for DLB. Behavioral problems in DLB are more frequent, more severe and appear earlier than in other neurodegenerative diseases and, together with other neuropsychiatric symptoms, contribute to impairment of quality of life of the patients, but their pathophysiology is poorly understood. Neuroimaging studies displayed deficits in cholinergic brainstem nuclei and decreased metabolism in frontal, superior parietal regions, cingulate gyrus and amygdala in DLB. Early RBD in autopsy-confirmed DLB is associated with lower Braak neuritic stages, whereas those without RBD has greater atrophy of hippocampus and increased tau burden. αSyn pathology in the amygdala, a central region in the fear circuitry, may contribute to the high prevalence of anxiety, while in attention dysfunctions the default mode and dorsal attention networks displayed diverging activity. These changes suggest that behavioral disorders in DLB are associated with marked impairment in large-scale brain structures and functional connectivity network disruptions. However, many pathobiological mechanisms involved in the development of behavioral disorders in DLB await further elucidation in order to allow an early diagnosis and adequate treatment to prevent progression of these debilitating disorders.