Approach Considerations
No sensitive or specific blood or urine tests are currently available for DLB. Laboratory studies in patients with dementia with Lewy bodies (DLB) should include those usually ordered in a dementia evaluation, including the following:
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Chemistry panel
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Complete blood count (CBC)
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Thyroid studies
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Vitamin B-12 levels
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Syphilis, Lyme disease, or human immunodeficiency virus (HIV) testing, when appropriate
Cerebrospinal fluid (CSF) examination is not required in routine cases. However, CSF findings in DLB include the following:
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Patients with Alzheimer disease have higher levels of tau protein in their CSF than do patients with DLB
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Patients with LB variant of Alzheimer disease (LBV-AD) have intermediate values
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CSF levels of beta amyloid are lower than normal in DLB, Alzheimer disease, and LBV-AD; however, CSF beta-amyloid levels in DLB, LBV-AD, and Alzheimer disease do not differ from each other [13]
Patients with DLB may have changes on electroencephalography earlier than do patients with Alzheimer disease, but whether this difference is diagnostically useful is not clear.
In certain circumstances, neuropsychological testing is helpful in differentiating DLB from Alzheimer disease and in establishing a baseline for future comparison. [14]
Imaging Studies
Because vascular dementia can cause symptoms and signs similar to those of DLB, brain magnetic resonance imaging (MRI) is indicated to distinguish DLB from vascular dementia. Patients with vascular dementia often have white matter lesions on MRI scans, whereas patients with DLB do not. [15]
Patients with DLB usually have less hippocampal atrophy than do patients with Alzheimer disease (but more than control subjects), although whether this difference is clinically useful is under investigation, as is the diagnostic utility of functional imaging. MRI is superior to computed tomography (CT) scanning in identifying this atrophy.
SPECT or positron emission tomography (PET) scanning may show decreased occipital lobe blood flow or metabolism in DLB but not in Alzheimer disease. SPECT using ligands that bind to the dopamine transporter molecule (eg,123 I-beta-CIT) has been used to suggest the diagnosis of DLB. Abnormal dopamine transporter scans have been shown to have a sensitivity of over 75% and a specificity of over 90% for DLB. [16]
A study by Lim et al using SPECT scanning with123 I-beta- carbomethoxy-3beta-(4-fluorophenyl) tropane (123 I-beta-CIT), as well as PET scanning with18 F-fluorodeoxyglucose (18 F-FDG), in 14 patients with a clinical diagnosis of DLB and 10 with Alzheimer disease found that relative preservation of the mid- or posterior cingulate gyrus (cingulate island sign) had 100% specificity for DLB. SPECT and PET scanning each appeared useful for the diagnosis of DLB, but SPECT provided more robust results than did PET. [17]
PET imaging with Pittsburgh Compound B showed that amyloid deposition in clinically diagnosed patients with DLB was similar to that in the patients with Alzheimer disease. However, amyloid binding was less in patients with dementia in Parkinson disease. Findings of these studies suggest that the presence of amyloid accelerates dementia in Lewy body disorders but has little influence on its nature. [18, 19]
Until disease-modifying therapies that are specific to DLB or Alzheimer disease are developed, metabolic imaging studies to enhance the accuracy of the diagnosis are rarely needed.
Histologic Findings
The characteristic lesion is the LB, an eosinophilic (hematoxylin and eosin staining), round inclusion found in the cytoplasm of substantia nigra cells and in the nucleus basalis of Meynert, locus ceruleus, and dorsal raphe, as well as in the dorsal motor nucleus of CNX. LBs are found in nonpyramidal cells in layers V and VI of the cortices (especially the limbic and transitional cortex).
Other histologic findings in DLB are minimal atrophy, occasional vacuolization in deep layers of the temporal cortex, and abnormal neurites in cells of CA2/3 of the hippocampus and various brainstem nuclei.
Other Tests
A new test, called the Lewy body composite risk score (LBCRS), may help determine whether Lewy body pathology is contributing to dementia. The checklist was derived from clinical features in autopsy-verified cases of healthy controls, Alzheimer’s disease (AD), DLB, and PD with and without dementia. It was tested and validated in a cohort of 256 patients. The LBCRS was able to discriminate DLB from other causes of dementia. [20, 21]
The test consists of 10 yes-or-no questions: 4 covering motor symptoms (slow movements, rigidity or stiffness, balance problems with or without falls, and a resting tremor) and 6 covering nonmotor symptoms (excessive daytime sleepiness, episodes of illogical thinking, frequent staring spells, visual hallucinations, acting out dreams, and orthostatic hypotension).
