ESSENTIALS OF DIAGNOSIS
Episodic or progressive multifocal symptoms and signs
Onset most often in otherwise healthy young adults
Abnormal findings on magnetic resonance imaging (MRI) of the brain (>95% of patients)
Multiple sclerosis (MS) is the leading cause of neurologic disability in young adults. Although not generally a fatal disease, the social impact of disability caused by MS is substantial. MS results in loss of employment, causes dependency on care providers, and often leads to social isolation. MS affects approximately 900,000 Americans and millions of individuals worldwide. Because MS is a chronic, disabling illness, multiple factors add to the societal burden of the disease, including disease-modifying and symptom-management medications, relapse treatment, hospitalizations for illnesses triggered by MS disabilities, loss of vocation and the need for supportive care for patients who become wheelchair or bedbound.
There is no single test to diagnose multiple sclerosis, and its cause is unknown. The diagnosis relies on recognition of the clinical patterns of the disease. Waxing and waning neurologic deficits that localize to the central nervous system are the hallmark of the disease in most patients. The diagnosis can be supported by laboratory studies, including MRI of the brain and spinal cord, analysis of cerebrospinal fluid (CSF), and evoked potential studies of the visual and somatosensory pathways. Systemic or infectious etiologies with similar presentations should be excluded.
MS affects only the central nervous system, sparing the peripheral nervous system from injury. The pathologic hallmark of MS is focal demyelination within the brain and spinal cord. Myelin is a cellular layer formed by oligodendroglial cells that wraps around and electrically insulates axons, thereby allowing saltatory conduction of axon potentials. In MS, discrete areas of damaged myelin called plaques are embedded within normal-appearing tissue. Within each plaque, damaged myelin is associated with inflammatory infiltrates of lymphocytes and macrophages, antibody and complement deposition, activated microglia, and oligodendroglial cell loss. Because of this pathologic association with inflammation and demyelination, MS is considered an autoimmune disease. It is not known whether the immune response observed in MS plaques is a primary process or secondarily caused by other possibilities, such as infectious, toxic, or metabolic etiologies.
There is no cure for MS, and all currently available treatments are only partially effective in reducing MS symptoms and disability. All MS therapies approved by the US Food and Drug Administration (FDA) alter immune function and reduce inflammation, adding support to the theory that MS is, at least in part, mediated by immune injury.
MS affects women two to three times as often as men. MS is rare in the pediatric population, but its risk increases steadily from adolescence up to the age of 35 and then gradually decreases. MS is rarely diagnosed after the age of 65.