What happens in multiple sclerosis, exactly?

What is it?

Multiple sclerosis (MS) is neurological disease. It is characterized by the loss of the insulating covers that allow electrical signals to pass in neurons.

MS can basically cause any neurological symptoms. The symptoms can either come in “attacks”; first worsening rapidly but improving afterwards; or they can worsen gradually. Perhaps the most common symptoms are fatigue, cognitive and emotional difficulties, and problems with vision, mobility and physical sensation.

Globally, MS affects around 30 people in 100 000. It typically onsets between the ages 20-50, and it’s more common in women.

What causes it?

The exact cause of MS is not known, but it is though to be a combination of a genetic vulnerability and environmental factors. Smoking and living far from the equator are associated with the risk of MS. Certain viral infections might also be a key factor in the development of the disease, but we’ll get back to that.

What happens during it?

Our immune system is very sophisticated. When it fights off a virus or a bacterium, it remembers the encounter as well as how to function efficiently in case of a future attack.

MS is thought to be an autoimmune disease. This means that the body mistakes it’s own cells for invaders and attacks them. Normally the body knows to leave its own cells alone, but this error in judgment could occur if the body was infected with a microbe that has a very similar surface protein structure to some of the body’s own cells. When the immune system fights the pathogen, it classifies that structure as something to destroy. In an unlucky situation, the body would then react in the same way to the body’s own cells as it learned to react to the microbe.

Our nervous system functions by sending electrical signals from one neuron to another through long “extensions” of the cell called axons. To help the neurons transmit these signals, their axons are surrounded by fatty layers known as myelin sheaths. These sheaths consist of cells called oligodendrocytes, and they are the things under attack in MS.

When the oligodendrocytes are first destroyed, they try to repair the myelin sheath, but are not able to succeed completely. When this process is repeated for sufficiently many times, the myelin sheaths are effectively replaced by scar-like plaques. This leads to the reduced ability of the neurons to conduct signals, and consequentially to the symptoms of MS.

When our immune system encounters a pathogen, it not only tries to destroy it specifically, but also more generally, and this is why MS also causes inflammation in the brain. This could lead to other potentially harmful consequences like swelling.

How can it be treated?

Unfortunately, there is currently no cure for MS. The treatment focuses on restoring function after an attack, preventing attacks, and relieving specific symptoms. This is mainly achieved through medications. In most patients the disease progresses to the point where they can’t walk independently, and the average age of death is 5 to 10 years lower than that in the general population.

 

 

Sources: https://en.wikipedia.org/wiki/Multiple_sclerosis, http://emedicine.medscape.com/article/1146199-overview#a3, http://www.nhs.uk/Conditions/Multiple-sclerosis/Pages/Treatment.aspx

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