Imaging and Diagnostic Criteria for Differentiating Lewy Body Dementia from Alzheimer’s Disease

Structural Imaging

MRI of the brain without contrast is recommended as the first‑line imaging study to rule out alternative causes and to evaluate characteristic structural patterns in patients with suspected dementia. The American College of Radiology guidance highlights its optimal use for this purpose【1】【2】.
In Lewy body dementia (LBD) the medial temporal lobe and hippocampi are relatively preserved, whereas Alzheimer’s disease (AD) typically shows marked atrophy of these structures. This pattern distinction is supported by radiologic analyses from two recent studies【1】【2】.
Loss of the “swallow‑tail” sign on susceptibility‑weighted imaging (SWI) has been observed in LBD patients, mirroring findings in Parkinson’s disease. The presence of this sign aids in supporting an LBD diagnosis【1】.

Fluorodeoxyglucose PET/CT (FDG‑PET) frequently reveals occipital‑lobe hypometabolism in LBD, a finding that differentiates it from the metabolic profile of AD. Evidence from multicenter imaging cohorts underpins this observation【1】【2】.
The “cingulate island sign” – preservation of FDG uptake in the posterior cingulate gyrus despite occipital hypometabolism – serves as a biomarker favoring LBD over AD, where posterior cingulate hypometabolism is typical. This sign has been validated in comparative PET studies【1】【2】.
DaTscan (I‑123 Ioflupane SPECT) demonstrates reduced dopamine‑transporter uptake in the striatum of LBD patients, with loss of the normal comma‑shaped appearance in the putamina. Diagnostic performance reaches approximately 78 % sensitivity and 90 % specificity for separating LBD from AD【1】【3】.

Amyloid PET/CT alone should not be used to differentiate LBD from AD because co‑existent amyloid pathology is common in LBD (up to 63 % of individuals older than 80 years)【2】.
The Society of Nuclear Medicine advises that brain amyloid PET/CT is rarely appropriate in patients with suspected LBD, emphasizing reliance on clinical and other imaging markers【1】.

A formal dementia diagnosis requires the presence of cognitive or behavioral symptoms that interfere with daily activities and represent a decline from prior functioning. Consensus criteria from the Alzheimer’s Association outline these requirements【4】【5】.
When imaging shows preserved medial‑temporal structures together with functional findings (occipital hypometabolism, cingulate island sign, abnormal DaTscan), the combined evidence strongly supports an LBD diagnosis.
In cases of brain‑stem‑predominant Lewy body disease with cognitive impairment, clinicians should consider additional co‑pathologies, as mixed neuropathology is common【6】.

All statements are derived from peer‑reviewed sources indicated by the citation IDs. No patient‑specific data are included.

The American College of Radiology recommends using the "1-year rule" for timing of cognitive symptoms relative to motor symptoms, combined with specific clinical features and imaging patterns to differentiate Lewy Body Dementia (LBD), Alzheimer's Disease (AD), and Parkinson's Disease Dementia (PDD) 7, 8

The American Academy of Neurology suggests that the timing of dementia onset relative to parkinsonism is a key differentiator: if cognitive impairment appears before or within 1 year of motor symptoms, diagnose DLB; if dementia develops after at least 1 year of well-established Parkinson's motor symptoms, diagnose PDD 7, 8
Fluctuating cognition with pronounced variations in attention and alertness is a core feature of LBD, assess using Mayo Fluctuations Scale or Clinician Assessment of Fluctuation 7, 8
Recurrent, well-formed visual hallucinations are a characteristic of LBD 7
REM sleep behavior disorder is a supportive feature for LBD 7

The Journal of the American College of Radiology recommends obtaining structural imaging first to exclude other causes, and notes that relative preservation of medial temporal lobe structures is seen in LBD compared to marked atrophy in AD 9, 8
DaTscan (I-123 Ioflupane SPECT) shows decreased dopamine transporter uptake in both LBD and PDD, but normal uptake in AD 9, 8
FDG-PET demonstrates occipital hypometabolism in LBD/PDD, while AD shows posterior cingulate and temporoparietal hypometabolism 9

Neocortical (diffuse) Lewy body disease is an adequate explanation for dementia in LBD 10, 11, 7
Brainstem-predominant Lewy body disease with cognitive impairment should prompt consideration of other contributing diseases 10, 11
Intermediate or High level AD neuropathologic change (ABC scoring system) is an adequate explanation for AD dementia 10, 11

The American College of Radiology suggests establishing dementia diagnosis by identifying cognitive or behavioral symptoms interfering with daily function 8
Determine the temporal relationship between dementia and motor symptoms to differentiate DLB and PDD 8
Assess core clinical features such as fluctuating cognition, visual hallucinations, and REM sleep behavior disorder 7, 8
Obtain imaging, starting with MRI to assess medial temporal lobe preservation vs. atrophy, followed by DaTscan if necessary 9, 8

Do not rely on amyloid imaging alone as LBD frequently has coexistent AD pathology 10, 9, 11
Avoid neuroleptics in suspected LBD due to severe sensitivity and risk of adverse effects 7, 8
Recognize that these conditions frequently overlap, with up to 50% of LBD cases having coexistent AD pathology 10, 11, 7