Question

If multiple sclerosis is a disease of the central nervous system, explain how clinical problems are related to demyelinization of axons.

Answer 1

Multiple sclerosis is a demyelinating disease  in which the immune system disrupts the protecting covering of nerves in brain and spinal cord causing a wide range of potential symptoms.

Normal Neuron with Myelin damaged myelin

Image 1: Normal neuron and demyelinated neuron

Causes/Risk factors:

• Some viral infections : Epstein-Barr virus
• Low level of Vit.D and less exposure to sunlight.
• People living in countries with temperate climate.
• Auto immune diseases : Thyroid , Type 1 diabetes and inflammatory bowel diseases.

Pathophysiology

Normally the myelin sheath protects the axon and helps in conduction of action potential and communication of sensory motor signals. but in Multiple Sclerosis, this protective covering is damaged resulting in various clinical symptoms. The process of demyelination is as follows:

Etiological factors (Genetic /Environmental/ Viral infection) $\Rightarrow$ Immune system mistakenly recognizes the myelin as foreign body   $\Rightarrow$ attacks the mylein proteins by macrophages   $\Rightarrow$ activation of cell mediated (T cells) and humoral (B cells) immunity   $\Rightarrow$ T cells releases Cytokines (mainly IL-17) and B cells and plasma cells releases Immunoglobulins (Oligoclonal auto antibodies) $\Rightarrow$ attack mylein sheath and Oligodendrocytes    $\Rightarrow$ Demyelination $\Rightarrow$ Decreased speed in action potential $\Rightarrow$ Sensory, Motor and Cognitive problems

Clinical manifestations :

Problems related to Motor Function

• Numbness or weakness in one or more limbs
• Lhermitte sign: Electric-shock sensations that occur with certain neck movements, especially bending the neck forward
• Tremor, Unsteady gait

Problems related to Sensory Function

• Partial or complete loss of vision
• Prolonged double vision
• Blurry vision
• Tingling or pain in parts of your body
• Problems with sexual, bowel and bladder function

others :

• Slurred speech
• Fatigue
• Dizziness

Conclusion

Multiple sclerosis is a potentially disabling disease of  the central nervous system. The main reason for the demyelination is considered to be an autoimmune reaction, where the body attacks its own cells.It is a long term disease.