Multiple Sclerosis (MS) is a chronic disease of the central nervous system (CNS). The body’s immune system mistakenly attacks myelin, the protective sheath surrounding nerve fibers. This attack causes inflammation and subsequent damage, resulting in areas of scarring called lesions. Lesions disrupt communication pathways between the brain and the rest of the body, leading to varied neurological symptoms. The location of these lesions within the CNS (brain, optic nerves, and spinal cord) largely determines the type of physical symptoms experienced.
The Role of MRI in Detecting MS Lesions
Magnetic Resonance Imaging (MRI) is the primary tool neurologists use to visualize the inflammatory damage and scarring caused by MS. MRI uses strong magnetic fields and radio waves to create detailed images of the brain and spinal cord tissues. MS lesions appear on standard T2-weighted sequences as bright spots (hyperintensities), indicating inflammation and demyelination. Brain imaging focuses on areas like the periventricular, juxtacortical, and infratentorial regions. Spinal cord imaging targets the cervical (neck) and thoracic (mid-back) sections, which are the most common sites for damage.
Spinal Cord Predominant MS
It is possible to have MS lesions in the spinal cord without any detectable lesions in the brain, a presentation sometimes called Spinal Cord Predominant MS. This manifestation is a recognized way the disease can present, particularly in the primary progressive form. Spinal cord lesions are highly prevalent in MS overall, with most patients showing these abnormalities over time. About 60% of spinal lesions are found in the cervical spine, but they can occur anywhere along the cord.
Symptoms resulting from spinal cord lesions relate directly to the affected nerves. Common complaints include motor weakness, stiffness, and spasticity, often affecting the legs and leading to difficulty walking. Sensory changes are frequent, manifesting as numbness, tingling, or Lhermitte’s sign (a feeling of electric shock when the neck is bent forward). Damage to these pathways also frequently causes issues with bladder and bowel function, such as urgency, retention, or constipation.
How MS is Diagnosed: Understanding Dissemination
A formal diagnosis of MS relies on the McDonald Criteria, which requires demonstrating that the disease has spread in both space and time. Dissemination in Space (DIS) requires evidence of lesions in at least two of the five characteristic CNS regions: periventricular, juxtacortical/cortical, infratentorial, spinal cord, and optic nerve. Dissemination in Time (DIT) requires evidence of new lesions appearing on a follow-up MRI or a second clinical attack.
For a patient presenting with only spinal cord lesions, the diagnosis can still be met. If imaging shows two or more spinal cord lesions, this is sufficient to fulfill the DIS requirement, even if brain scans are clear. In cases with a single clinical attack and only one area of CNS damage, a diagnosis can be confirmed if supporting evidence is found, such as specific findings in the cerebrospinal fluid.
Conditions That Mimic Spinal MS
The initial presentation of MS with isolated spinal lesions is challenging because several other conditions cause similar inflammation and damage. A thorough differential diagnosis process is necessary to rule out these possibilities. One important mimic is Neuromyelitis Optica Spectrum Disorder (NMOSD), which often causes severe optic nerve inflammation and extensive spinal cord lesions spanning three or more vertebral segments.
Other conditions include Transverse Myelitis (TM), which involves a single episode of inflammation across one section of the spinal cord. Acute disseminated encephalomyelitis (ADEM) and systemic autoimmune conditions like Lupus or Sarcoidosis must also be considered. Blood tests for specific antibodies, such as Aquaporin-4 (AQP4) or Myelin Oligodendrocyte Glycoprotein (MOG), are often necessary to distinguish NMOSD and MOG-associated disease from MS, as treatments differ significantly.