From the Guidelines
A normal DAT scan result essentially excludes Parkinsonian syndromes, including Parkinson's disease, as it demonstrates the presence of normal dopamine transporter levels in the brain. A DAT scan measures dopamine activity in the brain by binding to dopamine transporters and can be used to demonstrate the loss of presynaptic dopaminergic neurons in Parkinson's disease 1. The scan can show decreased radiotracer uptake in the striatum, usually in a posterior to anterior direction from the putamen to the caudate nuclei, which is characteristic of Parkinson's disease and some related disorders. Some key points to consider when interpreting DAT scan results include:
- A normal I-123 ioflupane SPECT/CT essentially excludes Parkinsonian syndromes, including Parkinson's disease 1
- DAT scans can demonstrate abnormal patterns of dopaminergic depletion for patients with Parkinson's disease, multiple system atrophy, progressive supranuclear palsy, and corticobasal degeneration 1
- The emergence of new nuclear medicine tracers, such as 11C-raclopride-PET and I-123-iodobenzamide SPECT scans, may play a role in the evaluation of patients with suspected Parkinson's disease in the future, but these are not yet approved for clinical use 1 It is essential to note that while a DAT scan is a valuable diagnostic tool, the diagnosis of Parkinson's disease still relies primarily on clinical evaluation by a neurologist, with the DAT scan serving as a supportive test rather than a definitive one.
From the Research
DAT Scan and Parkinson's Disease Diagnosis
- A DAT scan can be useful in determining if nigrostriatal dopaminergic degeneration (NSDD) is present, which is a characteristic of Parkinson's disease 2.
- The scan can help differentiate Parkinson's disease from other non-degenerative parkinsonian disorders, such as essential tremor, dystonic tremor, drug-induced, and psychogenic parkinsonism 3.
- However, a normal DAT scan does not completely rule out Parkinson's disease, as false negative scans can occur 3, 4.
Clinical Scenarios for DAT Scan Use
- DAT scans 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.
- The scan can also be useful in determining underlying NSDD in patients with a Parkinson's disease diagnosis for 3-5 years but without apparent clinical progression or development of motor fluctuations 2.
- In cases of drug-induced parkinsonism, DAT-SPECT imaging can improve diagnostic certainty and guide decision-making 4.
Limitations of DAT Scan
- The sensitivity of the DAT scan is limited by the clinical diagnosis, and false negative scans can occur 3.
- Clinical assessment remains the most important aspect in evaluating patients with suspected parkinsonism, and the DAT scan should be used in conjunction with a thorough neurological examination 3, 5.
- The DAT scan has limited value in differentiating among degenerative causes of parkinsonism 3.