Parkinson’s disease is a progressive neurodegenerative disorder that affects movement. An MRI (magnetic resonance imaging) scan can be used to help diagnose Parkinson’s disease, but it may not always detect the disease in its early stages.
Can an MRI detect Parkinson’s disease?
An MRI scan is often used to rule out other conditions that may cause similar symptoms as Parkinson’s disease. It can detect structural changes in the brain that may be indicative of Parkinson’s, but these changes may not be present early on.
In the early stages of Parkinson’s disease, an MRI scan may appear normal and not show any abnormalities. As the disease progresses over years or decades, MRI can begin to show characteristic findings:
- Loss of pigmented neurons in the substantia nigra – This area deep in the brain is responsible for producing dopamine and is damaged in Parkinson’s disease. The loss of pigmented neurons can appear as lighter shading on MRI.
- Iron accumulation in the basal ganglia – Excess iron deposits can build up in areas like the substantia nigra and show dark shading on MRI.
- Atrophy or shrinkage of brain structures – Over time, subtle loss of volume or shrinking can occur in areas like the midbrain.
However, even later in the disease, the MRI changes may be very mild or ambiguous. So while an MRI can sometimes detect features suggestive of Parkinson’s, the findings are often inconclusive, especially early on.
Reasons an MRI may not detect Parkinson’s
There are a few key reasons why Parkinson’s disease may not show up on an MRI scan:
- Not sensitive early in disease – MRI detects structural changes in the brain, but early Parkinson’s is more of a biochemical imbalance with functional changes that precede structural damage. So very early disease often has a normal looking MRI.
- Findings can be subtle – Even later on, the MRI changes associated with Parkinson’s are often mild or ambiguous and can be missed by radiologists.
- Variability in disease progression – The changes on MRI correlate with nerve cell loss, but the rate and pattern of progression varies tremendously between individuals.
- Many mimics of Parkinson’s – Other disorders like Lewy body dementia and progressive supranuclear palsy can mimic Parkinson’s but have different MRI findings.
So while MRI can sometimes help diagnose more advanced Parkinson’s disease, normal MRI findings do not rule out Parkinson’s, especially early on. The diagnosis is based more on the clinical symptoms.
Role of MRI in diagnosing Parkinson’s
Although MRI may not directly detect evidence of Parkinson’s disease, it still plays an important role in the diagnosis by ruling out other possible causes. Some examples of how MRI helps include:
- Exclude brain tumor – MRI helps definitively rule out the possibility of a brain tumor causing symptoms that mimic Parkinson’s disease.
- Rule out stroke – MRI can detect old silent strokes that could result in parkinsonism.
- Assess white matter disease – MRI shows any white matter changes that may indicate vascular parkinsonism.
- Detect atypical parkinsonism – MRI may reveal characteristic findings of multiple system atrophy, progressive supranuclear palsy, or other atypical syndromes.
So while MRI does not diagnose Parkinson’s disease directly in most cases, normal MRI findings help increase diagnostic confidence by excluding other potential causes for the symptoms.
Other imaging tests for Parkinson’s
In addition to MRI, other imaging techniques may occasionally be used to help diagnose Parkinson’s disease:
- DAT scan – This SPECT scan uses a radiotracer to assess dopamine transporter binding levels in the brain. Reduced binding can confirm a Parkinson’s diagnosis but does not indicate severity.
- PET scan – PET detects metabolic activity and can show reduced dopamine levels in Parkinson’s. It is not used routinely but may help in complex cases.
- CT scan – CT is generally less sensitive than MRI but on rare occasions may reveal characteristic brain changes of Parkinson’s disease.
However, most patients will not require additional scanning beyond a standard MRI. These other scans may be reserved for ambiguous cases.
Typical MRI protocol for Parkinson’s diagnosis
When MRI is performed to evaluate possible Parkinson’s disease, doctors typically order a standard protocol to maximize detection of any structural abnormalities. This usually includes:
- T1-weighted images – Shows gray/white matter differentiation and atrophy patterns
- T2-weighted images – Reveals demyelination, infarction, iron accumulation
- FLAIR – Highlights white matter hyperintensities and structural lesions
- Gradient echo sequences – Sensitive for mineralization and iron deposits
- Contrast enhancement – Helps characterize any enhancing masses or lesions
Images are carefully reviewed for subtle signs of neurodegeneration in regions like the basal ganglia, midbrain, pons and medulla. So while Parkinson’s itself may not show up, other characteristic findings can point towards the diagnosis.
Parkinson’s treatments do not change MRI findings
It is important to understand that treatments for Parkinson’s disease do not significantly alter the structural changes seen on MRI. This includes medications like levodopa, surgery like deep brain stimulation, and other therapies. While they may improve symptoms, they do not reverse or prevent the neuronal loss and brain atrophy over time that MRI detects.
Therefore, the expectations of MRI do not change much even after Parkinson’s treatment is initiated. Serial MRIs over time will continue showing gradually progressive changes as the disease runs its course. The aim of therapy is to improve function despite the ongoing neurodegeneration.
Role of MRI in monitoring Parkinson’s progression
Sequential MRI scans obtained over many years can help provide an objective measure of Parkinson’s disease progression in an individual. However, MRI changes lag behind the actual onset and advancement of symptoms.
Some of the MRI features that tend to progress over time include:
- Decreased substantia nigra volume
- Atrophy of the pons, cerebellum and other brainstem structures
- Dilation of the third ventricle
- Cortical thinning in frontal and temporal lobes
These quantitative markers seen on serial MRI may provide supplemental information about disease stage along with clinical markers. However, symptoms and examinations remain the primary way of gauging progression and adjusting treatment.
Conclusions
In summary, while MRI scans are commonly performed during the diagnostic workup for Parkinson’s disease, they do not definitively diagnose or exclude Parkinson’s in most cases.
MRI is unable to directly detect the biochemical changes occurring in early Parkinson’s disease. It can only identify structural changes in the brain, which may not appear until later stages.
However, a normal MRI is still useful to rule out other sinister causes of parkinsonism and lend support to a Parkinson’s diagnosis when symptoms are characteristic. MRIs may also have a role in monitoring disease progression over time.
But for early diagnosis, clinical acumen remains key, and the absence of MRI abnormalities should not deter or delay initiating appropriate treatment.
References
Here are some references used as sources for this article:
- Rizzo G, Copetti M, Arcuti S, Martino D, Fontana A, Logroscino G. Accuracy of clinical diagnosis of Parkinson disease: A systematic review and meta-analysis. Neurology. 2016 Feb 9;86(6):566-76.
- Brooks DJ. Imaging approaches to Parkinson disease. J Nucl Med. 2010 Apr;51(4):596-609.
- Antonini A, Benti R, De Notaris R, Tesei S, Zecchinelli A, Sacilotto G, Meucci N, Canesi M, Mariani CB, Pezzoli G. 123I-Ioflupane/SPECT binding to striatal dopamine transporter (DAT) uptake in patients with Parkinson’s disease, multiple system atrophy, and progressive supranuclear palsy. Neurol Sci. 2003 Jun;24(1):149-50.
- O’Neill, J. Imaging Parkinson’s disease. BMJ. 2017 Aug 10;358:j3224.