Introduction: Dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD) are two subtypes of Lewy body dementia (LBD) that share many clinical features such as visual hallucinations, cognitive impairment, and parkinsonism. Despite these similarities, both DLB and PDD can vary in the severity, frequency and onset of these symptoms. Therefore, a differential diagnosis between the two subtypes is needed to optimize symptom management and patient care. Today, the fundamental difference between DLB and PDD is based upon the chronological sequence of motor and cognitive deficits and their onset. In DLB, cognitive deficits precede parkinsonian motor symptoms by one year, whereas PDD is diagnosed when cognitive deficits develop after motor impairments (known as the “1-year rule”). Besides this “1-year rule”, current research has shown subtle, yet unclear, differences that could help distinguish between these two subtypes. Therefore, this literature review will examine and summarize neurological, cognitive, and clinical differences between DLB and PDD.
Methods: Informed by three databases, a literature search for peer-reviewed, empirical studies was conducted. In total, eight articles were examined for this review that directly compared a DLB clinical group with a PDD group.
Results: Neuroanatomical differences in cortical atrophy, cerebral angiopathy, functional connectivity, fluid biomarkers overlapping with Alzheimer’s disease, and alpha-synuclein were observed. Clinical and cognitive differences include frequent delusions and hallucinations, more severe dementia symptoms and poorer independent functioning for DLB. In contrast, people with PDD tend to have more tremors, but better orientation and visual memory.
Discussion: Despite these neurological, cognitive, and clinical differences between the two subtypes, no reliable or valid biomarker has been shown to confidently and accurately distinguish DLB from PDD. However, the synthesis of this research will be helpful to clinicians in conducting differential diagnoses by considering the potential underlying differences between PDD and DLB. As well, this literature review will be beneficial for researchers looking to further study these two LBD subtypes.
Conclusion: Given the heterogeneous nature of different types of dementia, further research is needed to validate these clinical differences to determine the prognosis of PDD relative to DLB, and to determine specific biomarkers for a definitive differential diagnosis.
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