Brain imaging and bioimaging for Parkinson’s Disease

Pathologisch (2)Normal (2)Bioimaging for Parkinson’s Disease (PD) could be useful, especially for those patients consulting for the first time and not fulfilling entirely the diagnostic criteria. I refer to patients with limited features of the disease (atypical tremor, predominant postural tremor, incertitude as the progression, missing or unclear data about the response to levodopa), patients with unusual features (lower-body predominant parkinsonism, falls, cognitive deficits, dysarthria or urinary symptoms at the beginning of the disease, inferior limb tremor, strictly unilateral disease, lack of asymmetry), or to patients with additional white matter hyperintensities or vascular lesions on the brain MRI. Even if the routine use of neuroimaging is not recommended in all patients with PD, for the first clinical evaluation, I almost always demand a brain MRI examination to a radiologist who is specialized in neuroradiology. Actually, for the first evaluation, there is almost always the patient’s request to confirm the clinical diagnosis with some additional data. Brain MRI could be useful to exclude subcortical or infratentorial tumors or malformations and, furthermore, to assess for white matter lesions (which could be responsible of some symptoms that will not respond to levodopa as dysarthria or lower-body predominant parkinsonism). Finally, MRI examination allows to detect, apart from vascular lesion, the presence of signs that are specific to parkinsonian disorder other than PD. These are the ‘hot-cross-bun” sign and the reduced MRI T2 signals of putamen in multiple system atrophy, and midbrain, superior and cerebellar peduncle atrophy in progressive supranuclear palsy. Brain MRI is necessary for younger patients to look for iron or calcium deposition in basal ganglia structures. Functional imaging of the dopamine transporter using SPECT and (123I) ioflupane (DaTscan) is a very useful tool to differentiate PD from essential tremor. The specificity of the DaTscan for PD is very high (93-97%). DaTscan is also normal in other mimics of PD such as drug-induced parkinsonism, psychogenic tremor, central nervous system infections or other autoimmune disorders, hydrocephalus, pallidal atrophies, X-linked dystonia– parkinsonism and dopa-responsive dystonia. However, it should be absolutely noted that the DaTscan results could be confounding in differentiating PD from other parkinsonian disorders (about 10% of cases), especially in the early phases of the diseases, when the clinical picture is incomplete. This could be case of the supranuclear progressive palsy or Lewy body disease or others. I always ask for a DaT-Scan in young patients with early onset PD. Actually, I should say that, against official recommendations of the neurologic associations, my “clinical threshold” for demanding a DaT-Scan is finally low. Often, also when the clinical picture could be sufficiently clear and diagnostic criteria are fulfilled, several patients, at the first evaluation, even when the brain MRI is normal, seem to request some instrumental or laboratory confirmation of the disease before starting a pharmacological treatment. This is the case when a so-called “political” Dat-Scan is performed. 123iodine-meta-iodobenzyl guanidine (123I-MIBG) myocardial scintigraphy, showing postganglnionic sympathetic cardiac denervation in PD could also distinguish PD from other causes of parkinsonism. Some other techniques are are in development. These techniques are the 7T-MRI scanning and transcranial sonography, examinations which detect directly the abnormalities of the substantia nigra. Do you use  “political” DaTscans?

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