Lewy Body Disease: Clinical and Pathological ``Overlap Syndrome'' Between Synucleinopathies (Parkinson Disease) and Tauopathies (Alzheimer Disease)

Lewy body disease (LBD) is a neurodegenerative disease resulting in dementia. It shares clinical and pathological features with Parkinson disease (PD), the most frequent synucleinopathy, Parkinson disease dementia (PDD), and Alzheimer disease (AD), a tauopathy. Even though the diagnostic criteria for these neurodegenerative diseases are clearly established, and recently revised for LBD, their precise clinical diagnosis is often difficult because LBD, PD, PDD, and AD share epidemiological, clinical, and pathological characteristics. This manuscript discusses current understanding of overlapping symptoms and the particular features of LBD, PD, and AD. It also describes features that could facilitate the diagnosis of each of these diseases. We concluded that the concept of neurodegenerative ``overlap'' syndrome, which includes the accepted diagnosis of LBD, may be taken in account and should contribute to clarifying LBD and definitions of close differential diagnoses. This should allow clinicians to suspect LBD at an earlier stage and provide better patient care.