Multiple sclerosis (MS) is an autoimmune disease that affects the central nervous system. It damages the myelin sheath that protects nerve fibers in the brain, spinal cord and optic nerves. This damage slows or blocks messages between the brain and body, leading to symptoms such as numbness, weakness, balance and coordination problems, vision loss, fatigue and cognitive issues.
Magnetic resonance imaging (MRI) is one of the key tools used to help diagnose MS and monitor its progression. MRI uses powerful magnetic fields and radio waves to create detailed images of organs and tissues inside the body. It can detect areas of inflammation, demyelination and nerve damage caused by MS.
What does an MRI show in MS patients?
In MS patients, MRI can reveal white matter lesions in the brain and spinal cord. These lesions represent areas where myelin has been damaged. On MRI images, they appear as bright spots or plaques.
Some key things an MRI may show in MS include:
- Lesions in the white matter of the brain, especially in regions like the periventricular area, corpus callosum, brain stem and cerebellum
- Lesions in the spinal cord, typically located in the cervical and thoracic regions
- Enhancement or swelling in active lesions with disruption of the blood-brain barrier
- Loss of brain volume or atrophy over time
- A higher lesion load or number of lesions
In some cases, MRIs may appear normal in people with early or mild MS. However, the scans can still provide valuable information by ruling out other potential causes of symptoms.
How accurate is MRI for diagnosing MS?
MRI is a very useful and accurate tool, though no single test can definitively diagnose MS. Guidelines say MRI findings can substitute for some criteria in establishing a diagnosis:
- If a scan shows lesions in typical MS locations, it can demonstrate CNS damage required for diagnosis
- Gadolinium-enhancing lesions help satisfy criteria for lesions that are disseminated in time and space
In one study looking at MRI accuracy, scans detected brain lesions consistent with MS in 88% of confirmed MS cases. Spinal cord lesions were seen in 79% of cases. The accuracy was lower in early stages, but increased with more MRI scans over time.
Overall, MRI detects about 5-10 times more lesions than a neurological exam. It can identify subclinical lesions and small changes missed through other tests. However, MRI results should always be interpreted in the full clinical context for each patient.
What types of spinal lesions can occur in MS?
Different types of lesions may appear on the spinal cord MRI of MS patients:
- Focal spinal cord lesions – These lesions affect localized areas of the spinal cord. They often occur in the cervical spine and upper thoracic region.
- Lesions spanning 3+ vertebral segments – Long lesions that extend over 3 or more vertebrae are fairly specific for MS.
- Peripheral nerve lesions – MS can sometimes affect spinal nerve roots emerging from the cord.
- LESCLs (longitudinally extensive spinal cord lesions) – These lesions span over 3 or more vertebral segments and tend to have poorly defined margins.
- Central gray matter lesions – Uncommon lesions found within the gray matter in the spinal cord center.
Identifying and tracking these lesion types on MRI provides useful information on MS progression and helps guide treatment.
What are the limitations of spinal MRI for MS?
While spinal cord MRI is an excellent tool in MS, it does have some limitations:
- Resolution is lower than brain MRI, making it harder to detect smaller lesions
- Spinal cord motion can create artifacts and image distortion
- Long scan times and confined space may cause discomfort for patients
- Lesions may not accurately reflect level of disability or impairments
- Scans may appear normal in early or mild disease stages
- Does not detect gray matter lesions as well as white matter lesions
Using high-field strength scanners (3T or more) and newer techniques like phase-sensitive inversion recovery sequences can help improve visualization of spinal cord lesions.
How often should MS patients get a spinal MRI?
There are no fixed guidelines on how frequently MS patients need to undergo spinal cord MRI. Some general recommendations include:
- 1-2 scans during initial diagnosis and workup
- Every 1-2 years to monitor disease progression
- When starting or changing disease-modifying therapies
- After a relapse or new/worsening symptoms appear
- Before starting any new treatments that require screening for spinal lesions
In most cases, brain MRI scans are performed more frequently than spinal scans for surveillance. However, adding periodic spinal cord imaging provides useful additional information for managing MS.
How are spinal lesions different from brain lesions in MS?
There are some key differences between spinal cord and brain lesions that are visible on MRI:
| Spinal Cord Lesions | Brain Lesions |
|---|---|
| Usually larger in size | Tend to be smaller |
| Can span multiple vertebral segments | Confined within anatomical regions |
| Might not enhance with contrast | Often demonstrate contrast enhancement |
| Lower lesion load overall | Higher total lesion burden seen |
| Less inflammatory features | More inflammation around active lesions |
| Harder to detect over time | New lesions can be spotted more readily |
These differences highlight the value of imaging both the brain and spinal cord to fully evaluate the effects of MS.
What are the advantages of a spinal MRI in MS?
Some benefits of using spinal cord MRI in MS patients include:
- Detects lesions that may explain symptoms even when brain appears normal
- Provides early evidence of disease activity and inflammation
- Allows assessment of lesion load and distribution in the cord
- Helps predict future disability and progression
- Guides treatment choices by identifying high-risk patients
- Monitors effects of therapies on lesion development
Though brain imaging remains essential, adding periodic spinal MRI gives a more complete view of MS disease activity and damage to optimize care.
Can spinal lesions appear without brain lesions in MS?
In most MS cases, both brain and spinal cord lesions are present. However, in a minority of patients, it is possible to have spinal lesions without detectable lesions in the brain, at least initially.
In one study, around 4% of MS patients had spinal cord lesions but normal brain MRI findings. The spinal lesions were predominantly located in the cervical cord.
Some reasons this can occur include:
- The brain lesions are very small or limited in number, escaping detection
- The scans are performed very early in the disease course before brain lesions develop
- The spinal cord is more susceptible to damage in some patients
- Technical factors like motion obscure brain lesions while spinal lesions are visible
So while spinal-only presentation is not common in MS, it points to the importance of imaging the cord in addition to the brain for the fullest view possible.
Conclusion
In summary, MRI is a highly useful test for diagnosing and monitoring MS, including assessing spinal cord involvement. Spinal lesions are common in MS and have some distinct features compared to brain lesions. Regular spinal cord imaging, in addition to brain MRI, provides added information on MS disease activity and progression that can optimize treatment.