As described by Merck Manual:
Disseminated patches of demyelination in the brain and spinal cord characterize multiple sclerosis. Common symptoms include visual and oculomotor abnormalities, paresthesias, weakness, spasticity, urinary dysfunction, and mild cognitive impairment. Typically, neurologic deficits are multiple, with remissions and exacerbations gradually producing disability
In simpler termsmultiple sclerosis is thought to be an inflammatory (degenerative) process involving the nerves of the brain and spinal cord, which destroys the fatty myelin sheaths around the nerve (axons) cells. This leads to demyelination and scarring of the nerve cells. As the name suggest Multiple sclerosis can involve different areas of the brain and spinal cord (central nervous system)at various points in time. Myelin sheath:Myelin provides a covering or insulation for nerves it acts by improving the conduction of impulses along the nerves and transmitting information in a timely manner. It is alsoimportant for maintaining the health of the nerves. If the myelin is disrupted (as in multiple sclerosis) in any way the transmitted information is not only delayed, but the brain may also misinterpret it.

• Multiple sclerosis is more common in individuals of northern European descent.
• Women are more than twice as likely to develop multiple sclerosis as men.
• Multiple sclerosis usually affects people between the ages of 20 and 50 years, and the average age of onset is approximately 34 years.

Multiple sclerosis occurs when the Myelin sheaththat covers the central nervous system (brain and spinal cord) is disrupted. This leads to delay of transmissions through the nerve cells.
Multiple sclerosis is believed to be an autoimmune disease meaning that the body own immune system attacks the myelin sheath producing patches of demylenation (also known as plaques). These plaques disrupt the transmission of information in the CNS and lead to the symptoms seen in multiple sclerosis.
The exact cause why this process occurs is not known. Experts believe that multiple sclerosis is caused by a combination of genetic, Environmental and infectious factors. Genetic: The risk of acquiring the disease is higher in relatives of a person having the disease.
Environmental

• Smoking
• Diet
• Stress
• Vaccinations

Infectious Causes: Certain viral infections like herpes and retrovirus

The symptoms of multiple sclerosis can vary greatly from person to person and time to time depending upon the degree of damage (demylenation) to the nerves. The symptoms also depend on which kind of nerve cells are involved if sensory nerve fibers are involved it causes sensory loss if those nerve fibers are affected that carry signals to muscles then problems with muscular movement occurs. Multiple sclerosis may progress and regress unpredictably. This happens due to repeated damage and repair of myelin sheaths. The person with MS can suffer almost any neurological symptom or sign, including changes in sensation such as loss of sensitivity or tingling, pricking or numbness but usually the first symptoms are of the eyes
Ocular (eye) Symptoms:

• Nystagmus
• Diplopia
• Optic Neuritis

Throat Symptoms:

• Dysphagia (difficulty in swallowing)
• Dysarthia(difficulty in speech)

Sensation:

• Pain
• Numbness
• Pricking

Muscular:

• Weakness
• Spasms
• Difficulties in coordination and movement (Ataxia)

Nervous System

• Depression
• Unstable mood
• Cognitive impairment
• Fatigue

Bowel:

• Incontinence
• Diarrhea or constipation

Urinary:

• Incontinence
• Increased frequency or retention

The diagnosing multiple sclerosis is difficult. The doctors usually have to combine history, physicalexamination, and tests to reach at a certain diagnosis. A complete blood count and spinal fluid examination may be done to rule out other diseases. A MRI scan is done to study the changes in the brain.

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