What is Multiple Sclerosis?

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Multiple sclerosis is a chronic inflammatory, autoimmune, and neurodegenerative disease of the central nervous system that affects the brain and spinal cord. Its main features are the appearance of lesions over the nerve fibres and their protective layer, the myelin sheath, a substance consisting of proteins and fats, which helps in the transmission of nerve impulses.

The immune system, which normally protects us from diseases, reacts incorrectly against myelin in many areas, occasionally leaving scars (sclerosis). These scarred areas (lesions) are also known by the name of demyelinating plaques.

These lesions are produced at different times, and in multiple locations in the brain and spinal cord. The symptoms and signs of the disease vary from one person to another depending on the areas affected. Although different people share the same diagnosis, the disease and its progression may be different in each case.

Types of multiple sclerosis

​​​​​​Multiple sclerosis is characterised by the appearance of episodes or flare-ups of neurological dysfunction that remains constant for 3-4 weeks and that are slowly recovered throughout the following month. It must always be a manifestation that does not coincide with a fever or any other state that could alter the general status.

These flare-ups do not always occur in the same way or with the same intensity, and may follow a different course. Based on these differences it may be considered that there are different sub-types of the disease.

Relapsing-remitting form. It is the most common form, with 8-9 of every 10 patients with multiple sclerosis having this progressive form. It is characterised by the appearance of episodes or flare-ups of neurological dysfunction from which the patient recovers completely or partially (thus the name remitting) and which are repeated every determined time (relapsing).

Primary progressive form. This affects around 1 in 10 patients and is characterised by a gradual deterioration in disability from the onset, without having flare-ups throughout the disease.

Secondary progressive form. The patients with relapsing remitting multiple sclerosis, after the first 15-20 years from the onset of the disease, enter a phase of gradual worsening of the neurological function, without being a result of a flare-up.

Progressive-relapsing form. It is less common. It is characterised by the constant progression of the disease since its onset, sometimes presenting during flare-ups.

How many people are affected by multiple sclerosis?

It is calculated that there are around 2.5 million people affected in the world. In the West, it is the most common chronic neurological disease in young adults. The frequency depends on the geographic location and genetic factors. Thus, it is more common between latitudes 40o and 60o north and south.

In Europe, the number of cases in the northern countries and the United Kingdom is around 2 for every 1,000 inhabitants, which is similar to that of the United States and Canada. In Spain, it is around 1 for every 1,000 inhabitants, which means that about 47,000 people are affected in our country. In Africa, Asia and South America, the disease is less common.

Multiple sclerosis can appear at any age, but it is rare before 10 years, and after 60 years. The average age of onset is at 30 years, with a first peak between 21 and 25 years, and another much lower one between 41 and 45 years. It affects females more than males, in a ratio of 2-3 to 1. In older age groups (over 45 years), the ratio is 1:1.

Substantiated information by:

Ana Hernando
Albert Saiz

Published: 20 February 2018
Updated: 20 February 2018

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