What is the role of PET scanning and SPECT in the evaluation of patients with Parkinson disease (PD)?

Updated: Aug 29, 2019
  • Author: Robert A Hauser, MD, MBA; Chief Editor: Selim R Benbadis, MD  more...
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Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) scanning are useful diagnostic imaging studies, but these are not routinely required. Different radioligands permit imaging of different components or abnormalities within the brain.

At the onset of motor signs, patients with Parkinson disease show an approximately 30% decrease in18 F-dopa (fluorodopa) uptake on PET imaging in the contralateral putamen.18 F-Dopa is taken up by the terminals of dopamine neurons and converted to18 F-dopamine. The rate of striatal18 F accumulation reflects transport of18 F-dopa into dopamine neurons and its decarboxylation to18 F-dopamine, which is stored in dopamine nerve terminals in the striatum. Thus,18 F-dopa PET imaging provides an index of remaining dopamine neurons. However, this study is not widely available, is usually not covered by insurance, and is currently generally considered a research tool.

Carbon-11 (11 C)-nomifensine and cocaine analogues such as123 I-beta-CIT (iodine-123-labeled carboxymethoxy-3beta-4-iodophenyl-nortropane) and123 I-FP-CIT (fluoropropyl-CIT) bind to dopamine reuptake sites on nigrostriatal terminals and provide an index of the remaining dopamine neurons. Ioflupane (123 I) (DaTscan) is a radiopharmaceutical agent that is indicated for striatal dopamine transporter visualization using SPECT brain imaging to assist in the evaluation of adults with suspected Parkinsonian syndromes (PSs). This agent may be used to help differentiate essential tremor from tremor due to PSs (idiopathic Parkinson disease [IPD] and Parkinson-plus syndromes [PPS]). [1] Analysis of data from 2 clinical trials demonstrated that the use of ioflupane with iodine-123 and single-photon emission computed tomography (SPECT) scanning to diagnose early-stage Parkinson's disease performed as well as clinical assessment at 1-year follow-up. [38, 39]

Deficits on123 I SPECT scans indicate a dopamine deficiency syndrome but do not differentiate Parkinson disease from atypical parkinsonisms, including multiple system atrophy (MSA) and progressive supranuclear palsy (PSP). Ioflupane SPECT imaging reveals a dopamine deficiency in Parkinson disease, MSA, PSP, corticobasal ganglionic degeneration, and Lewy body disease. This study is normal in essential tremor, dystonic tremor, medication-induced parkinsonism or tremor, psychogenic disorders, and in normal individuals.

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