Etiology and Pathophysiology

MS is a chronic inflammatory demyelinating and neurodegenerative disease of the CNS which inhibits conduction of nerve impulses. In the CNS, the myelin sheath is a membranous extension of specialized cells called oligodendrocytes. These membranous extensions form a barrier that insulate and support and nerve axons of the brain and spinal cord.

The velocity or speed of impulse transmission is faster through myelinated axons. Non-myelinated axons conduct impulses very slowly. Healthy myelinate nerves can conduct impulses 50 times faster than non-myelinated nerves. MS causes axons to lose their covering of myelin, a process known as demyelination. Demyelination disables axons, making them unable to conduct stimuli rapidly or effectively.

"MS lesions evolve differently during early versus chronic disease phases, and within each phase, different plaque types and plaques in different stages of demyelinating activity are evident. Histologically, several basic processes drive the formation of plaques: inflammation, myelin breakdown, astrogliosis, oligodendrocyte injury, neurodegeneration and axonal loss, and remyelination" (Popescu B. 2013).

The etiology of multiple sclerosis (MS) remains unknown but multiple factors have been identified: immune dysfunction, genetic predilection, environmental factors and infectious agents.

Immune system connection:

• infiltration of MS lesions by T-cells, macrophages and B-cells
• cerebral spinal fluid Immunoglobulin G (IgG) is elevated above serum levels in 90% of MS patients
• serum anti-human herpesvirus type 6 (roseola) antibodies is strongly association with early MS
• effective drug treatments have been immune modifying medications.

Genetics (NMSS)

• The average person in the United States has about one in 750 (.1%) chance of developing MS.
•  For first-degree relatives of a person with MS, such as children, siblings or non-identical twins, the risk rises to approximately 2.5-5% with the risk being potentially higher in families that have several family members with the disease.
•  The identical twin of someone with MS (who shares all the same genes) has a 25% chance of developing the disease. If genes were solely responsible for determining who gets MS, an identical twin of someone with MS would have a 100% chance of developing the disease; the fact that the risk is only one in four demonstrates that other factors, including geography, ethnicity and the elusive infectious trigger, are likely involved as well.

Environment (healthline)

Epidemiologists have seen an increased pattern of MS cases in countries located farthest from the equator. People who live near the equator are exposed to more ultraviolet B radiation, This correlation causes some to believe that vitamin D may play a role. Vitamin D benefits immune system function.

Infection (NMSS)

"Many viruses and bacteria — including measles, canine distemper, human herpes virus-6, Epstein-Barr virus (EBV), and Chlamydia pneumonia — have been or are being investigated to determine if they are involved in the development of MS.  EBV, the virus that causes mononucleosis, has received significant attention in recent years. A growing number of research findings indicate that previous infection with EBV contributes to the risk of developing MS."

References:

healthline. 4 Possible Causes of Multiple Sclerosis (MS). Retrieved 11/9/2019. https://www.healthline.com/health/multiple-sclerosis/possible-causes

Popescu, B. F., Pirko, I., & Lucchinetti, C. F. (2013). Pathology of multiple sclerosis: where do we stand?. Continuum (Minneapolis, Minn.), 19(4 Multiple Sclerosis), 901–921

National Multiple Sclerosis Society (NMSS) https://www.nationalmssociety.org/What-is-MS/Who-Gets-MS Retrieved 11/9/2019

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