In which of the following conditions has SPECT shown reduced D2 receptor density?
The reduced dopamine receptor density seen in Lewy body dementia may explain the neuroleptic sensitivity associated with the condition.
Alzheimer's dementia15%Dementia caused by thyroid deficiency5%Frontotemporal dementia15%Lewy body dementia58%Vascular dementia6%
The reduced dopamine receptor density seen in Lewy body dementia may explain the neuroleptic sensitivity associated with the condition.
Neuroimaging dementia
Neuroimaging is used in dementia to exclude organic causes and to support a diagnosis (the term support is used as imaging techniques are not diagnostic in dementia).
Alzheimer's disease
Structural changes -
The primary role of MRI (and CT for that matter) in the diagnosis of Alzheimer's disease is the assessment of volume change in characteristic locations.
The two most relevant findings are:
- mesial temporal lobe atrophy (particularly hippocampus and entorhinal cortex)
- temporoparietal cortical atrophy
(ventricular enlargement is also seen which is a consequence of atrophy)
Dilatation of the perihippocampal fissure is a useful radiologic marker for the initial diagnosis of Alzheimer's disease, with a predictive accuracy of 91%.
Functional changes -
SPECT demonstrates temporoparietal hypoperfusion.
PET demonstrates temporoparietal glucose hypometabolism. With disease progression, frontal involvement may be evident.
Vascular dementia
Structural changes - CT and MRI demonstrate atrophy, infarcts, and extensive deep white matter lesions.
Functional changes - SPECT shows a patchy multi-focal pattern of hypoperfusion.
Lewy body dementia
Structural changes - Changes tend to be non-specific and subtle on structural imaging (hence functional imaging SPECT and PET often used). On CT and MRI ventricular enlargement is seen with relative preservation of medial lobe structures. White matter changes similar to Alzheimer's disease are also seen.
Functional changes - SPECT shows posterior deficits and reduced D2 receptor density.
Frontotemporal dementia
Structural changes - CT and MRI show frontal lobe atrophy
Functional changes - SPECT shows anterior perfusion deficits.
NICE
NICE recommend the following:
- Magnetic resonance imaging (MRI) is the preferred modality to assist with early diagnosis and detect subcortical vascular changes, although computed tomography (CT) scanning could be used.
- Perfusion hexamethylpropyleneamine oxime (HMPAO) single-photon emission computed tomography (SPECT) should be used to help differentiate Alzheimer's disease, vascular dementia and frontotemporal dementia if the diagnosis is in doubt.
- Dopaminergic iodine-123-radiolabelled 2-carbomethoxy-3-(4-iodophenyl)-N-(3-fluoropropyl) nortropane (FP-CIT) SPECT (aka DaTscan) should be used to help establish the diagnosis in those with suspected dementia with Lewy bodies (DLB) if the diagnosis is in doubt
