Multiple sclerosis (MS) is a complex, long-lasting neurological condition that affects the brain and spinal cord. This autoimmune disease involves the immune system mistakenly attacking myelin, the protective fatty sheath around nerve fibers. Damage to myelin disrupts communication pathways between the brain and the rest of the body, leading to symptoms such as muscle weakness, fatigue, and issues with coordination. Medical imaging, especially magnetic resonance imaging (MRI), is important for understanding MS, helping to identify lesions, measure disease progression, and evaluate treatment effectiveness.
Imaging Techniques for Multiple Sclerosis
Magnetic Resonance Imaging (MRI) is the preferred imaging method for multiple sclerosis due to its ability to create detailed pictures of the central nervous system. Unlike X-rays or CT scans, MRI does not use radiation; instead, it employs strong magnetic fields and radio waves. Different MRI sequences provide varying details about tissues. T2-weighted images are highly sensitive for detecting demyelinating lesions, which appear as bright spots due to increased water content where myelin has been damaged. Fluid-Attenuated Inversion Recovery (FLAIR) sequences are also commonly used, as they suppress the signal from cerebrospinal fluid, making it easier to see lesions near fluid-filled areas in the brain. T1-weighted images are useful for identifying chronic lesions, which can appear as dark spots, sometimes referred to as “black holes,” potentially indicating permanent tissue damage.
A contrast agent is often injected into a vein during an MRI scan. This agent helps highlight areas of active inflammation where the blood-brain barrier has been disrupted. Gadolinium-enhancing lesions appear as bright spots on T1-weighted images, indicating recent or ongoing inflammation. While MRI is the primary imaging tool, other techniques like Optical Coherence Tomography (OCT) assess retinal nerve fiber layer thinning, which can be affected in MS and may correlate with brain atrophy and disability. CT or PET scans are generally less common for diagnosing MS.
What Imaging Shows in Multiple Sclerosis
Demyelinating lesions are frequently found in specific locations within the central nervous system, including the periventricular regions (around the ventricles), juxtacortical areas (near the brain’s outer surface), infratentorial regions (brainstem and cerebellum), and the spinal cord. Lesions are characterized as either acute (active) or chronic. Active lesions, indicative of ongoing inflammation, enhance with a contrast agent on T1-weighted images. In contrast, chronic lesions do not enhance with contrast and can appear as T1 hypointense lesions, or “black holes,” which may signify irreversible tissue damage and axonal loss.
Beyond focal lesions, brain atrophy, or shrinkage of brain tissue, is another finding in MS, observable on MRI scans. Brain atrophy can occur early in the disease course and progresses faster than in healthy individuals. This loss of brain volume, particularly in deep gray matter structures, is associated with increased physical and cognitive disability, making it an important indicator of disease progression. Spinal cord lesions are also a common finding in MS, and their presence can correlate with increased disability and a higher risk of relapses.
Role of Imaging in MS Diagnosis and Monitoring
Imaging plays a major role in the initial diagnosis of multiple sclerosis, primarily through MRI. The McDonald criteria, widely used for MS diagnosis, incorporate specific MRI findings to establish evidence of “dissemination in space” (lesions in multiple areas of the central nervous system) and “dissemination in time” (new lesions appearing over time). For instance, the simultaneous presence of gadolinium-enhancing lesions (active inflammation) and non-enhancing lesions on a single MRI scan can fulfill the dissemination in time criterion.
MRI also assists in distinguishing MS from other neurological conditions that may present with similar symptoms or imaging findings, such as migraine or small vessel ischemic disease. Radiologists look for specific characteristics of MS lesions, such as their typical locations and shapes, to differentiate them from other conditions. In cases where brain MRI findings are not conclusive, imaging of the spinal cord can be particularly helpful in demonstrating dissemination in space.
For monitoring disease progression, follow-up MRI scans are regularly performed to detect new lesions, changes in existing lesion burden, and progression of brain atrophy. New or enlarging T2-hyperintense lesions or gadolinium-enhancing lesions indicate ongoing disease activity. While new lesions and overall brain atrophy have traditionally been monitored, recent research suggests that the atrophy of brain lesions themselves may be a more accurate predictor of long-term disability progression. Imaging also helps assess the effectiveness of disease-modifying therapies (DMTs) by observing a reduction in new lesion activity and a slower rate of brain atrophy. A decrease in new lesions or a stable MRI over time can indicate a positive response to treatment.