What are the DAT (Dopamine Transporter) scan findings?

From the Guidelines

A DAT scan typically shows reduced uptake of the radiotracer in the striatum, often asymmetrically, with the putamen more affected than the caudate nucleus, indicating a loss of dopaminergic neurons in the substantia nigra, as demonstrated by I-123 ioflupane SPECT/CT Brain scans 1. The DAT scan findings are used to differentiate Parkinsonian syndromes, such as Parkinson's disease (PD), multiple system atrophy (MSA), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD), from essential tremor and drug-induced tremor.

• The scan works by binding to the dopamine transporters, demonstrating the loss of presynaptic dopaminergic neurons in PD, and showing decreased radiotracer uptake in the striatum, usually in a posterior to anterior direction from the putamen to the caudate nuclei 1.
• A normal I-123 ioflupane SPECT/CT essentially excludes Parkinsonian syndromes, as it demonstrates normal dopamine transporter activity 1.
• The role of new nuclear medicine tracers, such as 11C-raclopride-PET and I-123-iodobenzamide SPECT scans, which target the postsynaptic dopamine receptors (D1 and D2), may grow in the future, but are not yet approved by the US FDA for clinical use 1. The DAT scan is particularly useful in distinguishing true parkinsonian syndromes from essential tremor or drug-induced parkinsonism, which typically show normal dopamine transporter activity.
• It is essential to discuss the DAT scan findings with a neurologist, who can interpret them in the context of clinical symptoms and other diagnostic information.
• The DAT scan cannot differentiate between Parkinson's disease, multiple system atrophy, and progressive supranuclear palsy, as all show similar patterns of reduced dopamine transporter density 1.

From the Research

DAT Scan Findings

• DAT scan findings can be useful in determining the presence of nigrostriatal dopaminergic degeneration (NSDD) in patients with clinically uncertain Parkinson's disease 2, 3, 4.
• The scan can help differentiate between Parkinson's disease and other non-degenerative parkinsonian disorders, such as essential tremor, dystonic tremor, and drug-induced parkinsonism 3.
• DAT scan results can be abnormal, normal, or inconclusive, with abnormal results indicating the presence of NSDD 2, 4.
• The percentage of patients with abnormal scan results can vary, with one study reporting 58.7% abnormal results 2 and another reporting 40% abnormal results 4.
• DAT scan findings can change clinical diagnosis and lead to changes in medication therapy, with one study reporting a change in diagnosis in 39.8% of patients and a change in medication therapy in 70.1% of patients 2.

Clinical Scenarios for DAT Scan Use

• DAT scan can be useful in patients with early subtle symptoms, suboptimal response to levodopa, prominent action tremor, drug-induced parkinsonism, and in patients with lower extremity or other less common parkinsonism clinical presentations 2.
• DAT scan can also be useful in determining underlying NSDD in patients with PD diagnosis for 3-5 years but without apparent clinical progression or development of motor fluctuations 2.
• DAT scan can be used to confirm the correct diagnosis and clinical management for patients with clinically indeterminate Parkinsonism 4.

Limitations and Future Directions

• DAT scan has limited value in differentiating among degenerative causes of parkinsonism 3.
• False negative scans can occur, highlighting the need for clinical follow-up 3.
• More long-term clinical studies are required to determine how DAT-SPECT scan can guide decision-making 3.
• The utility and cost-effectiveness of DAT scan as a diagnostic and prognostic tool in patients with parkinsonian symptoms in rare neurodegenerative diseases need to be determined in the future 5.