What are the key clinical features that differentiate Dementia with Lewy Bodies from Alzheimer's disease?

Differentiating Dementia with Lewy bodies (DLB) from Alzheimer's disease (AD) relies on several key clinical features.

• Cognitive Fluctuations: A hallmark of DLB is pronounced fluctuations in cognition, attention, and alertness, which are less typical in AD (McKeith et al., 2005).
• Recurrent Visual Hallucinations: Well-formed and detailed recurrent visual hallucinations are a core feature of DLB, often appearing early in the disease course (McKeith et al., 2005). While hallucinations can occur in AD, they are generally less frequent and tend to appear later in the disease progression (Jellinger, 2018).
• Spontaneous Parkinsonism: Motor symptoms such as bradykinesia, rigidity, and tremor, characteristic of Parkinsonism, are core features of DLB and often emerge within one year of cognitive decline (McKeith et al., 2005; Gomperts, 2016). In contrast, Parkinsonism is not a primary feature of AD and, if present, typically manifests much later in the disease course (Jellinger, 2018).
• Antipsychotic Sensitivity: People with DLB are highly sensitive to antipsychotic medications, which can worsen their motor features and lead to severe adverse reactions ¹. This sensitivity is not a characteristic of AD ¹.
• Memory Impairment: While memory impairment is prominent in AD, particularly verbal episodic memory ², it may be less severe in early DLB, with more pronounced deficits often seen in executive function and visuospatial abilities (Gomperts, 2016).

Specialist investigations can also aid in differentiation; for suspected DLB, I-FP-CIT SPECT or I-MIBG cardiac scintigraphy may be used if the diagnosis is uncertain ¹,². For suspected AD, FDG-PET, perfusion SPECT, or cerebrospinal fluid examination for tau and amyloid proteins can be considered ¹,². Structural imaging like MRI or CT scans are used to rule out reversible causes of cognitive decline and assist with subtype diagnosis in both conditions ¹,². However, a diagnosis of DLB should not be ruled out solely based on normal I-FP-CIT SPECT or I-MIBG cardiac scintigraphy results ². Similarly, AD should not be ruled out based solely on CT or MRI scans ².