MRI Findings in Parkinson's Disease
MRI brain imaging in Parkinson's disease is typically normal or shows only nonspecific age-related changes, as the diagnosis remains primarily clinical based on motor symptoms. 1, 2
Primary Role of MRI in Parkinson's Disease
MRI serves to exclude alternative diagnoses rather than confirm Parkinson's disease, as the structural imaging findings are usually unremarkable in early PD. 1, 3 The American College of Radiology recommends MRI brain without IV contrast as the optimal structural imaging modality when clinical presentation is unclear or atypical features are present. 1
What MRI Typically Shows in PD:
Normal or minimal findings - Most patients with early Parkinson's disease have normal-appearing brain MRI, which is why the diagnosis remains clinical. 1, 2, 4
Age-related changes only - Nonspecific white matter changes and mild generalized atrophy may be present but are not diagnostic of PD. 2, 4
No specific diagnostic markers - Conventional MRI sequences demonstrate limited abnormalities specific for Parkinson's disease. 4
Critical Diagnostic Purpose of MRI
The main clinical utility of MRI is excluding conditions that mimic Parkinson's disease, including:
Structural lesions - Tumors, subdural hematomas, or focal brain lesions that could cause parkinsonian symptoms. 1, 3
Vascular parkinsonism - Multiple lacunar infarcts or extensive white matter disease suggesting cerebrovascular etiology. 1, 2
Normal pressure hydrocephalus - Ventricular enlargement with characteristic imaging features (Evans index >0.3, enlarged temporal horns, callosal angle <90 degrees). 3
Atypical parkinsonian syndromes - MRI can support alternative diagnoses when red flags are present clinically. 1, 2
MRI Findings Suggesting Alternative Diagnoses
When MRI shows specific abnormalities, consider these atypical parkinsonian syndromes instead of idiopathic PD:
Progressive Supranuclear Palsy (PSP) - Midbrain atrophy ("hummingbird sign"), superior cerebellar peduncle atrophy, and third ventricular enlargement. 1
Multiple System Atrophy (MSA) - Putaminal atrophy with T2 hypointensity rim, "hot cross bun" sign in the pons, middle cerebellar peduncle hyperintensity, and cerebellar atrophy. 1, 2
Corticobasal Degeneration (CBD) - Asymmetric cortical atrophy, particularly in frontoparietal regions. 1
Advanced MRI Techniques (Research Context)
While not recommended for routine clinical diagnosis, advanced MRI techniques show promise in research settings:
Susceptibility-weighted imaging (SWI) - May detect increased iron deposition in substantia nigra, though this requires higher field strength magnets and is not standardized for clinical use. 4
Diffusion tensor imaging (DTI) - Research shows diffusional changes in orbital-frontal regions in pre-motor PD, but lacks clinical validation. 4
Functional MRI (fMRI) - Not recommended for clinical diagnosis of PD. 5, 4
MR spectroscopy - Not recommended for initial evaluation of parkinsonian syndromes. 5
When to Order MRI in Suspected PD
Order MRI brain without contrast when:
- Clinical presentation is atypical or uncertain. 1
- Red flags suggest alternative diagnoses (early severe autonomic dysfunction, cerebellar signs, pyramidal signs, vertical gaze palsy, symmetric onset, rapid progression). 1
- Patient has risk factors for structural lesions or vascular disease. 2
- Symptoms are not responding appropriately to dopaminergic therapy. 1
Functional Imaging for Parkinson's Disease
I-123 ioflupane SPECT/CT (DaTscan) is the gold standard functional imaging study when differentiation from non-degenerative causes is needed:
- Shows decreased dopamine transporter uptake in the striatum (putamen more than caudate) in PD. 5, 1
- A normal DaTscan essentially excludes parkinsonian syndromes, making it valuable for distinguishing PD from essential tremor or drug-induced parkinsonism. 1
- Abnormal in both PD and atypical parkinsonian syndromes, so cannot differentiate between them. 5
Common Clinical Pitfalls
Expecting MRI to confirm PD diagnosis - This is incorrect; PD diagnosis is clinical, and MRI is typically normal. 1, 6, 2
Ordering contrast-enhanced MRI routinely - IV contrast is not necessary for initial evaluation of suspected PD. 5, 1
Relying on MRI alone without specialist evaluation - General neurologists or movement disorder specialists should confirm the diagnosis, as correctly diagnosing parkinsonian syndromes on clinical features alone is challenging. 1
Ordering amyloid or tau PET/CT - These have no role in evaluating parkinsonian syndromes. 1