From the Guidelines
A normal Dopamine Transporter (DAT) scan essentially excludes Parkinsonian syndromes, including Parkinson's disease, with high accuracy. This is based on the findings of a 2020 study published in the Journal of the American College of Radiology, which states that a normal I-123 ioflupane SPECT/CT, a type of DAT scan, essentially excludes Parkinsonian syndromes 1. The scan works by using a radioactive tracer that binds to dopamine transporters, allowing visualization of the dopamine system integrity and demonstrating the loss of presynaptic dopaminergic neurons in Parkinson's disease.
When interpreting the results of a DAT scan, it is essential to consider the clinical symptoms and neurological examination findings, as a small percentage of patients with early Parkinson's disease may initially have a normal DAT scan 1. Additionally, the scan cannot rule out atypical parkinsonian syndromes that might mimic Parkinson's symptoms. However, the high sensitivity of the DAT scan, around 95%, makes it a valuable tool in differentiating Parkinsonian syndromes from essential tremor and drug-induced tremor.
Some key points to consider when using DAT scans in clinical practice include:
- A normal DAT scan strongly suggests that the patient does not have true Parkinson's disease
- The scan should always be interpreted alongside clinical symptoms and neurological examination findings
- A small percentage of patients with early Parkinson's disease may initially have a normal DAT scan
- The scan cannot rule out atypical parkinsonian syndromes that might mimic Parkinson's symptoms
- The high sensitivity of the DAT scan makes it a valuable tool in differentiating Parkinsonian syndromes from other conditions 1.
The emergence of new nuclear medicine tracers, such as 11C-raclopride-PET and I-123-iodobenzamide SPECT scans, may provide additional tools for evaluating patients with suspected Parkinson's disease in the future 1. However, these tracers are yet to be approved by the US FDA for clinical use and their role in the evaluation of patients with suspected Parkinson's disease is still evolving.
From the Research
Dopamine Transporter Scan Results
- A normal Dopamine Transporter (DAT) scan does not entirely rule out Parkinson's disease, as some patients with old-onset Parkinson's disease may have normal DAT-SPECT results despite having dopaminergic degeneration 2.
- Studies have shown that a normal DAT scan can suggest an alternative diagnosis such as essential tremor, vascular parkinsonism, drug-induced parkinsonism, or psychogenic parkinsonism 3.
- DAT imaging is abnormal in idiopathic Parkinson's disease, multiple system atrophy, and progressive supranuclear palsy, but does not distinguish between these disorders 3.
Clinical Implications
- DAT-SPECT imaging can be useful in determining if nigrostriatal dopaminergic degeneration is present, particularly in patients with early subtle symptoms, suboptimal response to levodopa, or prominent action tremor 4.
- A normal DAT scan result can lead to changes in management, including stopping or changing dopaminergic medications, and can help confirm an alternative diagnosis 5, 6.
- In some cases, a normal DAT scan result may not be conclusive, and repeat scanning may be necessary to confirm the presence or absence of dopaminergic degeneration 2.
Diagnostic Uncertainty
- DAT-SPECT imaging can help resolve diagnostic uncertainty in patients with clinically uncertain Parkinson's disease, but may not always provide a definitive diagnosis 4, 5.
- Clinical characteristics alone are often unreliable in distinguishing between Parkinson's disease and drug-induced parkinsonism, and DAT-SPECT imaging can provide additional information to guide diagnosis and management 6.