Multiple Sclerosis (MS) is a chronic condition that affects the central nervous system. It involves damage to the myelin sheath, a protective covering around nerve fibers in the brain, spinal cord, and optic nerves. This damage leads to areas of scarring or inflammation known as lesions or plaques, which disrupt the transmission of signals within the nervous system.
Lesions in the Spinal Cord Versus the Brain
MS lesions can indeed occur in the spinal cord even without visible lesions in the brain. While brain lesions are very common in MS, spinal cord lesions are also a significant and frequent feature of the disease. Approximately 20% of patients with spinal lesions do not have intracranial plaques.
Magnetic Resonance Imaging (MRI) is a crucial tool for detecting these lesions in both the brain and spinal cord. The presence of spinal lesions, even in the absence of brain lesions, does not rule out an MS diagnosis if other clinical criteria are met. Spinal cord abnormalities are common in suspected MS and may occur asymptomatically.
How Lesion Location Influences MS Diagnosis
The diagnosis of MS typically relies on demonstrating “dissemination in space” (DIS) and “dissemination in time” (DIT) based on the McDonald criteria. Dissemination in space means that lesions are found in at least two different areas of the central nervous system. These areas include periventricular, juxtacortical, infratentorial brain regions, and the spinal cord.
The presence of a spinal lesion can fulfill one of the required locations for dissemination in space, even if brain lesions are not present. Dissemination in time indicates that lesions have appeared at different points in time, which can be shown by new lesions on follow-up MRI scans or through clinical attacks. A diagnosis can be made based on clinical presentation, MRI evidence, or a combination of both.
Clinical Manifestations of Spinal Lesions
Lesions in the spinal cord can lead to specific symptoms depending on their location. Motor symptoms commonly include weakness, spasticity, and problems with gait or coordination. Sensory symptoms are also frequent, such as numbness, tingling, pain, or electric shock-like sensations like Lhermitte’s sign.
Bladder and bowel dysfunction, such as urinary control or constipation, are common symptoms of spinal cord involvement. These symptoms impact daily life. While brain lesions can cause cognitive issues or visual problems, spinal lesions are linked to physical impairments, and symptoms may persist.
Implications for Disease Course
The presence and extent of spinal cord lesions can influence MS progression. A higher burden of spinal cord lesions, particularly early in the disease course, is associated with greater physical disability progression. Prominent spinal cord lesions, especially in the lateral columns, are associated with MS progression.
While MS disease course is variable, understanding lesion location helps clinicians anticipate challenges. Treatment strategies aim to reduce lesion formation and progression throughout the CNS to mitigate disability. Patients without spinal cord lesions are less likely to experience disability accumulation.