Multiple Sclerosis (more commonly referred to as 'MS') is an autoimmune, degenerative neurological disease. It most commonly affects women, starting in their thirties, from a European and Caucasian background - but of course, it can develop in anybody. Why it has this female preponderance is still up for debate. However, many studies suggest that low levels of Vitamin D (received from sunlight) increases one's risk - perhaps explaining the incidence in pale Europeans. 

In our general overview, we discussed the neuron - a special type of cell that forms connections and transmits information in the form of electricity. An axon is the name for an elongated section of a neuron (like a long wire). The longest axon stretches from your lower back to your toe! To improve the speed of transmission, the wires are coated in an insulating sheath called myelin. 

The central nervous system (CNS) includes the brain and the spinal cord. All the other nerves that branch from here are part of the peripheral nervous system. MS only affects the CNS. Why you ask? Good question. Here's a simple answer. 

Myelin (the insulator for the wires) is produced in the CNS by cells called oligodendrocytes.
Myelin in the peripheral nerves is produced by Schwann cells. 
When the immune system incorrectly attacks the nervous system, it attacks oligodendrocytes, the myelin it produces, and the axon the myelin is insulating. The Schwann cells and the peripheral nerves are ignored. 
Therefore, only the CNS is affected by the inappropriate inflammation. 

With the potential to affect any region of CNS neurons - a wide array of symptoms can arise. It can be hard for doctors to make a definitive diagnosis with an isolated neurological incident. As a result, two different types of neurological dysfunction separated by time are required to make the diagnosis of MS. Many tests are performed to support the diagnosis - including an MRI of the brain and spinal cord (looking for white plaques), a sample of cerebrospinal fluid will be tested for 'unmatched oligoclonal bands' and an optic nerve latency test may be performed (measuring how fast an image is transmitted from the eyes to the image centre in the back of the brain). 

Why the optic nerve? Very commonly, the myelin sheath around the optic nerve is affected by MS - and patients often first lose the ability to see the colour red as vibrantly as before (known as red desaturation). In a progressed phase, the vision can become blurred. On the topic of vision, MS patients can sometimes develop double vision. This is usually due to an attack of the MLF (Medial Longitudinal Fasiculus) - a nerve that helps co-ordinate the eyes to move left and right together.  

There are three clinical subtypes of MS, based on the trajectory of the symptoms: Relapsing Remitting, Primary Progressive and Secondary Progressive. 

RR is the most common subtype - An immune system attack occurs with a loss of function, then there is no attack for a while...some patients may even make a full recovery before another attack occurs. Despite these periods of remission, eventually the multiple attacks take their toll and the overall level of disability will progress over time. 

SP usually follows from a period of RR, in which the inflammation doesn't go into a period of remission - and the patient experiences a steadier, more uniform decline. 

PP is a subtype of MS in which the patient never has periods of remission, the inflammation progresses from the onset of symptoms. 

MS is a common neurological ailment, and vast sums of money are spent on research and development of treatments - meaning an ever-improving landscape of pharmaceuticals. There are basic things most MS patients will receive, such as high dose Vitamin D. The other drugs aim to block the body's immune system from destroying the oligodendrocytes, the myelin sheath, the axons and ultimately the nerves of the central nervous system.