Imaging Recommendations for Parkinsonian Syndromes

First‑Line Structural Imaging (MRI)

MRI of the brain without intravenous contrast is the preferred initial structural study for evaluating Parkinsonian syndromes because it provides superior soft‑tissue detail and is more sensitive to iron deposition than CT. (American College of Radiology) 2 – moderate evidence
MRI can identify regional atrophy patterns characteristic of atypical Parkinsonian disorders (multiple system atrophy, progressive supranuclear palsy, corticobasal degeneration) that help separate them from idiopathic Parkinson disease. (American College of Radiology) 1 – moderate evidence
MRI also serves to exclude alternative etiologies such as focal lesions, vascular disease, or secondary causes of parkinsonism. (American College of Radiology) 1, 3 – moderate evidence
Susceptibility‑weighted imaging may reveal the “swallow‑tail” sign in the dorsolateral substantia nigra, a potential marker of Parkinson disease, although its diagnostic accuracy is still under investigation. (American College of Radiology) 4, 5 – low‑moderate evidence
Intravenous contrast is generally unnecessary for the initial work‑up unless an infectious or inflammatory process is specifically being considered. (American College of Radiology) 2 – moderate evidence

I‑123 ioflupane SPECT/CT is the most valuable functional imaging test for Parkinsonism and is essential for differentiating true degenerative Parkinsonian syndromes from clinical mimics such as essential tremor or drug‑induced tremor. (American College of Radiology) 1, 3 – strong evidence
A normal ioflupane scan effectively rules out Parkinsonian syndromes, making it especially useful when the clinical diagnosis is uncertain. (American College of Radiology) 1, 3 – strong evidence
The scan can detect dopaminergic neuron loss early, often before structural abnormalities appear on MRI or CT. (American College of Radiology) 1 – moderate evidence
Degenerative Parkinsonian disorders show a characteristic posterior‑to‑anterior decrease in radiotracer uptake within the striatum (greater loss in the putamen than the caudate). (American College of Radiology) 1, 2 – moderate evidence
Ioflupane SPECT confirms nigrostriatal degeneration but cannot differentiate among specific Parkinsonian subtypes (PD, MSA, PSP, CBD) because all exhibit abnormal dopaminergic depletion patterns. (American College of Radiology) 1, 3 – moderate evidence

FDG‑PET/CT has limited but specific utility for distinguishing progressive supranuclear palsy from idiopathic Parkinson disease by revealing a distinct metabolic pattern. (American College of Radiology) 1, 3 – limited evidence
In PSP, FDG‑PET typically shows hypometabolism in the medial frontal and anterior cingulate cortices, the striatum, and the midbrain—findings that are absent in idiopathic Parkinson disease. (American College of Radiology) 1, 5 – limited evidence
Despite widespread clinical use, the overall quality of evidence supporting FDG‑PET for Parkinsonism remains limited. (American College of Radiology) 1, 4 – low evidence

CT of the head is not the preferred modality for Parkinsonism because it provides inferior soft‑tissue characterization compared with MRI. (American College of Radiology) 1, 4, 3 – moderate evidence
When MRI is contraindicated, CT can still be employed to exclude structural lesions or vascular disease and may demonstrate regional volume loss patterns suggestive of atypical Parkinsonian syndromes (MSA, CBD, PSP). (American College of Radiology) 1, 3, 5 – moderate evidence
Routine use of intravenous contrast with CT is generally not indicated in the evaluation of Parkinsonian syndromes. (American College of Radiology) 1 – moderate evidence

Current literature provides no evidence to support the routine use of amyloid PET/CT, MR spectroscopy, or functional MRI in the initial evaluation of Parkinsonian syndromes. (American College of Radiology) 1, 2 – no evidence

Imaging should complement, not replace, a thorough clinical assessment; diagnosis of Parkinsonian syndromes remains primarily clinical. (American College of Radiology) 1, 5 – strong evidence
Early in disease, MRI may appear normal because structural changes often lag behind clinical symptoms, particularly in idiopathic Parkinson disease. (American College of Radiology) 2 – moderate evidence
While I‑123 ioflupane SPECT confirms the presence of nigrostriatal degeneration, it does not specify which Parkinsonian subtype is present. (American College of Radiology) 1, 3 – moderate evidence