Multiple Sclerosis

Definition

Multiple Sclerosis (MS) is a chronic autoimmune demyelinating disease of the central nervous system (CNS), characterized by inflammation, demyelination, and axonal damage leading to neurological deficits that vary in time and location.

Epidemiology

• Global prevalence: 2–150 per 100,000, highest in Northern Europe and North America.
• Onset typically between ages 20–40 years.
• Women are affected approximately 2–3 times more than men.
• Relapsing-remitting form is the most common initial presentation.
• Genetic predisposition: first-degree relatives have increased risk.

Etiology

• Autoimmune response against CNS myelin and oligodendrocytes.
• Environmental factors: low vitamin D levels, Epstein-Barr virus infection, smoking.
• Genetic susceptibility: HLA-DRB1*15:01 allele strongly associated.
• Combination of genetic and environmental factors triggers immune-mediated demyelination.

Pathophysiology

• Auto-reactive T cells cross the blood-brain barrier, initiating inflammation.
• Demyelination of CNS neurons leads to impaired nerve conduction.
• Axonal injury contributes to permanent neurological deficits.
• Formation of plaques (sclerotic lesions) in white matter of brain and spinal cord.
• Relapses due to active inflammation; progression due to neurodegeneration.