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 DAT-SPECT: useful for DLBvAD, not DLBvPD 
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Post DAT-SPECT: useful for DLBvAD, not DLBvPD
This review article is about the use of DAT-SPECT -- dopamine transporter SPECT scans -- in diagnosing movement disorders. The authors have done a great job in reviewing all the data and then presenting understandable one-sentence conclusions.

For DLB, the authors conclude: "DAT-SPECT cannot discriminate between PD/PD-dementia and DLB but can be very useful in the differential diagnosis between DLB and Alzheimer disease and can also be of some value in the differential diagnosis between DLB and vascular dementia."

I remember learning back in 2008 that there was some type of legal issue with bringing SPECT scans to the US, though they are already widely used in Europe. SPECT imaging is important for some disorders (such as DLB) so it's been frustrating that SPECT imaging is not approved for use in the US except in a few research settings. In 2008, there was a Q&A with Dr. Mark Stacy from Duke about this:

"Question: Why are SPECT scans not available in the US?
Answer: Because of corporate changes. GE bought Amersham (sp?). Amersham wanted to bring another type of SPECT agent to market. It's been found that the drug that GE started to bring to market in Europe is easier to use. So it got slowed down bringing this agent to the US. GE is talking to the FDA about using European trial data."

Recently, I asked Dr. Hubert Fernandez (on NPF's "Ask the Doctor" Forum) about the status of bringing DAT-SPECT scans to the US. He first explained what a DAT ligand is and then answered the question:

"DAT (dopamine transporter) is a type of ligand (vehicle or medium) to conduct the SPECT scan. [It] 'tags' dopamine. It is important that the medium used is the correct one. Good examples are altropane or B-CIT....these are ligands that are used for SPECT scans to evaluate for PD.

Yes, for now, they DAT SPECT scans are not commercially available....but soon they they will be. One of the companies that manufactures a DAT ligand has received an 'approvable letter' from the FDA."

OK, that's probably all any of you want to know about DAT-SPECT imaging.

I've copied the article's abstract and related excerpts below, if any of you want to go further...

Robin



Journal of Neurology, Neurosurgery & Psychiatry. 2010 Jan;81(1):5-12.

The role of DAT-SPECT in movement disorders.

Kägi G, Bhatia KP, Tolosa E.
Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, National Hospital for Neurology and Neurosurgery, London, UK.

Dopamine transporter (DAT) imaging is a sensitive method to detect presynaptic dopamine neuronal dysfunction, which is a hallmark of neurodegenerative parkinsonism. DAT imaging can therefore assist the differentiation between conditions with and without presynaptic dopaminergic deficit.

Diagnosis of Parkinson disease or tremor disorders can be achieved with high degrees of accuracy in cases with full expression of classical clinical features; however, diagnosis can be difficult, since there is a substantial clinical overlap especially in monosymptomatic tremor (dystonic tremor, essential tremor, Parkinson tremor).

The use of DAT-SPECT can prove or excludes with high sensitivity nigrostriatal dysfunction in those cases and facilitates early and accurate diagnosis.

Furthermore, a normal DAT-SPECT is helpful in supporting a diagnosis of drug-induced-, psychogenic- and vascular parkinsonism by excluding underlying true nigrostriatal dysfunction.

This review addresses the value of DAT-SPECT and its impact on diagnostic accuracy in movement disorders presenting with tremor and/or parkinsonism.

PubMed ID#: 20019219 (see pubmed.gov for abstract only)



Excerpts (in case you didn't get enough already):

"Dementia with Lewy bodies
In dementia with Lewy bodies (DLB), the extent of DAT loss in the striatum is in the range of PD and therefore not useful in the differential of PD and atypical PD. Neuropathological data suggest that 50-­60% of dementia in people aged 65 or older is due to Alzheimer disease, with a further 10­-20% each attributable to DLB or vascular cognitive impairment. Operationalised clinical diagnostic criteria have been agreed for all of these syndromes, but even in specialist research settings, they have limited accuracy when compared with neuropathological autopsy findings. Distinguishing Alzheimer disease from DLB is clinically relevant in terms of prognosis and appropriate treatment. A striking biological difference between DLB and Alzheimer disease is the severe nigrostriatal degeneration and consequent DAT loss that occurs in DLB, but not to any significant extent in Alzheimer disease. Several imaging
studies have shown that DAT imaging improves diagnostic accuracy with a sensitivity of 78% and a specificity of up to 94% in the separation between DLB and AD. Most of these studies have used clinical diagnosis as the gold standard, and the results have to be taken with some caution. One study with 20 cases with pathologically proven dementias (DLB/non-DLB) and with an FP-CIT SPECT at initial clinical workup showed that the DAT imaging substantially enhanced the accuracy of diagnosis of DLB by comparison with clinical criteria alone. Abnormal DAT imaging has therefore also been included as a suggestive feature in the DLB consensus criteria in 2005."


Thu Jan 07, 2010 12:37 am
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