Dementia with Lewy Bodies (DLB) is the second most common cause of neurodegenerative dementia in the elderly, accounting for between 10% and 30% of autopsied cases. Pathological and clinical features of DLB overlap with Alzheimer's disease (AD) and Parkinson's disease (PD), confounding the characterization of the disorder. Accordingly, an international consortium of experts developed diagnostic criteria to improve the antemortem identification of people who likely have the disease. The identification of these core features and the subsequent development of the consensus criteria for the clinical diagnosis of DLB have reportedly improved diagnostic accuracy (i.e., 83% sensitivity and 95% specificity). Yet, as many as 30% of autopsied DLB patients do not exhibit any core features during life. The frequent absence of key criteria necessitates the search for additional means of identifying patients with DLB. Improving diagnostic precision is particularly important since DLB patients may demonstrate a heightened response to cholinesterase inhibitors, may be particularly sensitive to neuroleptic medications, and may experience a different clinical course than patients with PD or AD. Visual cognition is a relatively unexplored domain that may be helpful for delineating clinical changes specific to DLB. Several neuropsychological studies with autopsy-confirmed patients have shown that DLB patients exhibit more severe deficits in visuospatial processing than well-matched AD patients. In fact, visuospatial deficits may be the best indicator of early DLB. However, visuospatial and constructional tests used to assess patients with DLB and AD frequently rely on skills unrelated to visual cognition, such as psychomotor speed, memory, and executive functioning, thus, confounding interpretation of poor performance on these tasks. Tests of basic visual cognition may be better suited for measuring the cognitive and pathological changes specific to DLB because they can be based on the relatively well-understood organization of the visual system. Direct comparisons with AD and PD patients are critical for differentiating the contributions of AD and Lewy body brain pathology in DLB. Because PD and DLB cause extrapyramidal motor signs and psychomotor slowing, excessive visual cognitive deficits in the DLB patients may be attributable to the cognitive, rather than motor, changes of DLB. If DLB and PD patients perform similarly on some of the visual tasks, and worse than AD patients, this pattern would suggest that the deficits result from pathological changes specific to Lewy bodies rather than to shared AD pathology or dementia in general. Detailed analysis and comparison of basic visual cognition in DLB, AD, and PD patients may reveal the components of visual cognition that are more affected by DLB than AD or PD, and may identify sensitive and specific cognitive measures that can effectively distinguish these disorders.
