Can Lewy Body Plaques Be Visualized on MRI?
No, Lewy body plaques themselves cannot be directly visualized on MRI scans, as these microscopic intracellular protein aggregates are far too small to be detected by current MRI technology.
Why Lewy Bodies Cannot Be Seen on MRI
Lewy bodies are intracellular inclusions composed of alpha-synuclein protein aggregates that are only visible at the microscopic level during histopathological examination 1, 2. The spatial resolution limitations of current MRI technology make direct visualization impossible:
- MRI resolution constraints: Current MRI has a maximum in-plane resolution of 500 to 780 µm 3
- Lewy body size: These pathological structures are microscopic intracellular inclusions that measure only a few micrometers in diameter 1, 2
- Location: Lewy bodies are preferentially located in limbic areas (particularly the amygdala) and throughout brainstem, limbic, and neocortical regions, but at a cellular level that is beyond MRI detection 2
What MRI Can Show in Dementia with Lewy Bodies
While Lewy bodies themselves are invisible on MRI, the imaging modality plays an important supportive role in the diagnostic workup 3:
Primary Role: Exclusion of Mimics
- MRI without IV contrast serves as a first-line test to exclude secondary causes such as subdural hematoma, brain tumor, or other structural lesions that could mimic dementia symptoms 3
Supportive Imaging Biomarkers
- Relative preservation of medial temporal lobe structures (particularly the hippocampus) is a supportive imaging biomarker according to the DLB consortium 3
- Hippocampal volume: Patients with DLB show significantly larger hippocampal volumes compared to Alzheimer's disease patients, though still smaller than healthy controls 4
- Pattern recognition: MRI hippocampal volumetry can help clinically discriminate DLB from Alzheimer's disease 4
Advanced MRI Techniques (Research Level)
- Diffusion tensor imaging (DTI): Can distinguish between different neurodegenerative disorders, including differentiating progressive supranuclear palsy from Lewy body disorders with high accuracy (area under the curve 0.96-0.97) 5
- MR spectroscopy: Limited data shows DLB patients may have decreased NAA/Cr ratios in occipital regions 3
Clinical Diagnostic Approach
The diagnosis of dementia with Lewy bodies relies on clinical criteria, not direct visualization of pathology 3, 1:
- Core clinical features: Fluctuating cognition, persistent visual hallucinations, and parkinsonism 1
- Imaging strategy: Use MRI to exclude structural mimics and identify supportive patterns of atrophy 3
- Functional imaging: Dopamine transporter SPECT (I-123 ioflupane) showing decreased striatal uptake is listed as a suggestive feature and has greater diagnostic utility than structural MRI 3
- FDG-PET: Can show characteristic occipital hypometabolism and the "cingulate island sign" 3
Important Caveats
- Definitive diagnosis requires autopsy: Lewy bodies can only be definitively identified through post-mortem histopathological examination 1, 2
- Clinical underdiagnosis: DLB is frequently misclassified as Alzheimer's disease, vascular dementia, or systemic delirium despite being responsible for 15-20% of all autopsy-confirmed dementias 1
- Coexisting pathology: Alzheimer's disease and Lewy body pathology commonly coexist, which can complicate both imaging interpretation and clinical diagnosis 3, 6