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DESCRIPTIONDopamine transporter imaging with single-photon emission computed tomography (DAT-SPECT) is being evaluated to improve the differential diagnosis of parkinsonian syndromes from non-parkinsonian tremor and of dementia with Lewy bodies (DLB) from Alzheimer disease.
Parkinsonian syndromes are a group of diseases that share similar cardinal signs, characterized by bradykinesia, rigidity, resting tremor, and gait disturbance. Parkinson disease (PD) is the most common cause of parkinsonism; however, diagnosing PD in early stage of the disease can be difficult. In addition, other etiologies such as essential tremor, corticobasal degeneration, multisystem atrophy, progressive supranuclear palsy, vascular parkinsonism, and drug-induced parkinsonism can lead to a similar set of symptoms. Even in specialized movement disorders centers, up to 25% of patients may be misclassified, and some patients, such as those with essential tremor who have been diagnosed with PD, may be erroneously treated. This has led to the development of additional tests to improve the accuracy of clinical diagnosis of PD and other parkinsonian syndromes. One recent approach is to evaluate the integrity of dopaminergic pathways in the brain using DAT-SPECT.
DAT-SPECT detects presynaptic dopaminergic deficit by measuring dopamine transporter (DAT) binding. In general, striatal DAT binding is reduced in PD, genetic parkinsonism, dementia with Lewy bodies (DLB), corticobasal degeneration, progressive supranuclear palsy, and multiple system atrophy, while striatal DAT binding is in the normal range in Alzheimer’s disease, essential tremor, dystonic tremor, orthostatic tremor, drug-induced parkinsonism, psychogenic parkinsonism, and vascular parkinsonism. It is proposed that an abnormal DAT-SPECT supports the diagnosis of PD or other neurodegenerative parkinsonian syndrome (multisystem atrophy, progressive supranuclear palsy), while a normal DAT-SPECT in a symptomatic patient increases the likelihood of a disease not affecting the nigrostriatal dopaminergic pathway.
Due to the degeneration of nigrostriatal neurons in DLB, DAT-SPECT is also proposed to differentiate DLB from Alzheimer’s disease. Some note a severe sensitivity to neuroleptics (potentially life-threatening) in patients with DLB. However, newer agents are usually well-tolerated, and patients with DLB may also respond to the cholinesterase inhibitors that are more commonly used to treat Alzheimer’s disease.
Analysis of DAT-SPECT images can be visual, semi-quantitative, or quantitative. Since patients typically do not become symptomatic before a substantial number of striatal synapses have degenerated, visual interpretation of the scan is thought to be sufficient for clinical evaluation. A variety of methods are being tested to improve the validity and reliability of ratings, including commercially available software to define the region of interest (ROI) for analysis and the development of an atlas for visual interpretation. Quantitative interpretation may aid visual interpretation and, if performed rigorously, may increase diagnostic accuracy; however, interobserver variability tends to be high with manual ROI-based semi-quantification. Semi-quantitative analysis also requires normal control values and varies across imaging systems.
Dopamine transporter ligands include 123I-β-CIT, 123I-FP-CIT, and 99mTc-TRODAT-1. 123I-β-CIT requires a delay between injection and scan of about 24 hours. 123I-FP-CIT (DaTscan™) is a fluoropropyl derivate of β-CIT that can be injected 3-6 hours before the scan.
DaTscan™ (GE Healthcare) has been in use in Europe since 2000 with a diagnostic indication for use in parkinsonian patients and with expanded use since 2006 in patients suspected of DLB. DaTscan was approved by the U.S. Food and Drug Administration (FDA) in 2011 and is “indicated for striatal dopamine transporter visualization using single photon emission computed tomography (SPECT) brain imaging to assist in the evaluation of adult patients with suspected parkinsonian syndromes (PS). In these patients, DaTscan may be used to help differentiate essential tremor from tremor due to PS (idiopathic Parkinson's disease, multiple system atrophy and progressive supranuclear palsy). DaTscan is an adjunct to other diagnostic evaluations.”
Related medical policies are –
Dopamine transporter imaging with single photon emission computed tomography (DAT-SPECT) is investigational for all indications, including but not limited to:
POLICY GUIDELINESInvestigative is defined as the use of any treatment procedure, facility, equipment, drug, device, or supply not yet recognized as a generally accepted standard of good medical practice for the treatment of the condition being treated and; therefore, is not considered medically necessary. For the definition of Investigative, “generally accepted standards of medical practice” means standards that are based on credible scientific evidence published in peer-reviewed medical literature generally recognized by the relevant medical community, and physician specialty society recommendations, and the views of medical practitioners practicing in relevant clinical areas and any other relevant factors. In order for equipment, devices, drugs or supplies [i.e, technologies], to be considered not investigative, the technology must have final approval from the appropriate governmental bodies, and scientific evidence must permit conclusions concerning the effect of the technology on health outcomes, and the technology must improve the net health outcome, and the technology must be as beneficial as any established alternative and the improvement must be attainable outside the testing/investigational setting.
The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.
POLICY HISTORY11/15/2012: Approved by Medical Policy Advisory Committee.
11/06/2013: Policy reviewed; no changes.
09/22/2014: Policy reviewed; no changes.
07/13/2015: Code Reference section updated for ICD-10.
02/10/2016: Policy description updated. The following investigational indications were updated in the policy statement: "essential tremor" changed to "distinguishing between parkinsonian syndromes and essential tremor" and "dementia with Lewy bodies" changed to "distinguishing between dementia with Lewy bodies and Alzheimer disease." Investigative definition updated in policy guidelines section.
05/31/2016: Policy number added.
SOURCE(S)Blue Cross Blue Shield Association policy # 6.01.54
This may not be a comprehensive list of procedure codes applicable to this policy.
Brain imaging, tomographic (SPECT)
Iodine I-123 ioflupane, diagnostic, per study dose, up to 5 millicuries