Comment on “Neuropsychological Comparison of Patients With Alzheimer’s Disease and Dementia With Lewy Bodies”

Dear Editor,

We enjoyed reading the original research paper by Kang et al.1 titled “Neuropsychological Comparison of Patients With Alzheimer’s Disease and Dementia With Lewy Bodies. Their comparative analysis of the cognitive profiles of the most common neurodegenerative diseases, Alzheimer’s disease (AD) and dementia with Lewy bodies (DLB), has provided a crucial foundation for understanding the pathophysiology of these conditions and how to effectively treat patients. The authors specifically divided the patients with AD into two groups based on the severity of coexisting parkinsonism, and conducted detailed analyses accordingly. The Unified Parkinson’s Disease Rating Scale (UPDRS) motor score was assessed in all patients, and among those with AD, UPDRS motor scores of 20 or higher were classified as AD^p+, while those with scores below 20 were classified as AD^p-. As movement-disorders specialists, we have some concerns about the possibility of other comorbidities being present in patients with AD classified as AD^p+.

We concur that parkinsonism is a frequently observed symptom in patients with AD.2 However, its severity is typically characterized by mild motor symptoms in those with AD.3 Mild parkinsonian signs are generally identified by UPDRS motor scores of up to 7 points. The criterion of a UPDRS motor score of 20 or higher used by Kang et al.1 should therefore be considered indicative of significant parkinsonism. Furthermore, the authors found that more than 50% of the patients with AD were classified as AD^p+. We were also curious about disease durations for patients with AD and DLB, which were not listed in the demographics table. If patients with AD^p+ are in the early stage, it would be necessary to check for dopaminergic loss through dopaminergic imaging. The possibility of comorbidity with Parkinson’s disease (PD) should be considered in those individuals. It would also be important to consider the use of antipsychotics and differentiate from drug-induced parkinsonism if a patient is in the advanced stages of AD. Moreover, it is important to assess the presence of vascular burden and confirm whether vascular parkinsonism has been investigated.

Not only all patients with AD but also a significant proportion of patients with DLB can exhibit positive results on amyloid imaging scans. Accordingly, these two clinical disorders should be differentiated through a comprehensive assessment of clinical symptoms and various tests. We were curious to determine whether the authors used the results of dopaminergic imaging as a criterion for differentiating between the two conditions, since dopaminergic imaging is known to be the most accurate method of distinguishing between AD and DLB.4 The authors also stated the following in the Methods section: “However, although the patients presented cognitive impairment, parkinsonism, and DAT depletion, they were not considered to have DLB if they did not experience cognitive fluctuation or visual hallucination.”1 We were curious about how those patients were handled, whether they were excluded from the study, or classified as AD, since there was no description of their status. If they were classified as AD^p+, the dual pathology of AD with PD cannot be ruled out. Alternatively, perhaps the authors classified those patients as PD with dementia, despite them meeting the diagnostic criteria for DLB.

Neurodegenerative disorders such as AD and DLB can be challenging to differentiate clinically, and may exhibit overlapping pathology in some cases. It is important to consider the possibility of comorbidity with PD, especially when significant parkinsonism is observed in AD.