Multiple Sclerosis Definition
Multiple sclerosis is a chronic, inflammatory, autoimmune disease of the central nervous system that causes widespread focal degradation of the myelin sheath, variable axonal and neuronal injury, and progressive disability in young adults. 1
Core Pathophysiology
- MS results from immune-mediated inflammation leading to demyelination with axonal transection throughout the central nervous system 2
- The disease process involves loss of the myelin sheath surrounding nerve axons, accompanied by variable degrees of axonal damage and neuronal injury 1
- Pathological features include inflammatory demyelination, axonal loss, gliosis, and the formation of characteristic sclerotic plaques in white and gray matter 3
Clinical Disease Subtypes
Relapsing-Remitting MS (RRMS):
- Affects approximately 85% of patients at disease onset 1
- Characterized by acute inflammatory relapses where nerve impulse conduction is disrupted, followed by remission phases with variable recovery 1
- Represents the most common initial presentation with acute onset of neurological symptoms developing over hours to days 4
- Over time, repeated relapses cause cumulative damage and scarring of myelin with progressive loss of neuronal function 1
Primary Progressive MS (PPMS):
- Affects approximately 15% of clinical cases 1
- Characterized by steadily increasing neurological disability from disease onset without distinct relapses or remissions 1, 4
- Pathogenesis involves progressive neurological damage rather than the relapsing-remitting pattern 1
Secondary Progressive MS:
- Develops when relapsing-remitting disease transitions to a phase of gradual disability accumulation affecting gait, coordination, and bladder function 5
Epidemiology and Demographics
- MS typically presents in young adults with mean age of onset between 20-30 years 2, 5
- Affects approximately 900,000 people in the United States 2
- Worldwide prevalence ranges from 5 to 300 per 100,000 people, with higher rates at increased latitudes 2
- Disproportionately affects women with a female-to-male ratio of nearly 3:1 2
- Life expectancy is reduced compared to the general population (75.9 vs 83.4 years) 2
Etiology
- The exact cause remains unknown, but research indicates a complex multifactorial etiology 1
- Contributing factors include genetic predisposition, immunological dysfunction, and environmental triggers such as viral exposures 1, 2
- Geography, vitamin D levels, hormones, and specific viral exposures all play documented roles in disease development 2, 5
Clinical Consequences
- Weight loss, malnutrition, and cachexia are well-recognized features in MS patients 1
- Common causes of nutritional decline include reduced mobility, fatigue, inappropriate diet, physical difficulty eating or drinking, poor appetite, visual impairment, cognitive decline, and dysphagia 1
- The disease leads to physical disability, cognitive impairment, and substantially decreased quality of life 2