What is MS?

Multiple sclerosis (MS) is a chronic, disabling neurodegenerative disease. It strikes most often during early adulthood, and most common neurological disorder among young adults and was thought to affect about twice as many women as men, although recent research points to an increase in this sex ratio to 4 : 1. Many aspects of MS, including its cause, are not well understood. It is unknown whether MS represents a single disease, or if its symptoms are the result of different diseases that have the same neurodegenerative effects. There is, however, a growing understanding of how the permanent physical and mental disabilities caused by MS arise over time.

MS is characterised by lesions in the central nervous system that interfere with nerve function. These lesions are inflammatory, meaning that immune cells that are normally restricted to the blood have migrated into the brain and the cellular partition between the brain and the blood stream (the blood-brain-barrier) has broken down. Local swelling occurs in the lesion site as cells and water move out of the blood stream into the nervous system tissue. This swelling causes problems with nerve function, because oedema and compression of the fibres can block electrical transmission along the nerve fibres. In addition, the immune cells in the lesion make chemicals that attack myelin, a fatty sheath made by support cells that surrounds nerve fibres (called axons). The myelin sheath supports the ability of neurons to transmit signals through the axon, and it provides special chemicals that neurons need to survive. When myelin is attacked and destroyed, the axon can compensate to some extent by rearranging signaling molecules in the denuded area, but the speed and strength of nerve signals traveling through the axon is impaired.

Image © 2005 Berlex Canada Inc.

Most of the time, in the early stages of MS, these inflammatory attacks occur over short intervals of acutely heightened disease activity. These episodes are followed by periods of recovery and remission. During the remission period, the local swelling in the nervous system lesion resolves, the immune cells become less active or inactive, and the myelin-producing cells remyelinate the axons. Nerve signaling improves, and the disability caused by the inflammation becomes less severe or goes away entirely. This phase of the disease is called relapsing-remitting MS(RRMS). The lesions do not all heal completely, though. Some remain as “chronic” lesions, which usually have a demyelinated core region which lacks immune cells. Over time, the cells in the center of such lesions mostly die, although inflammation often continues at their edges. People believed for many years that mainly the myelin was destroyed during the acute attacks and the axons were spared. Recent research has shown this is not the case. Even from the very beginning of MS onset, some of the nerve fibres that cross the lesion are damaged to the point that the axons are severed. This is fatal to the neuron. Broken axons in the brain cannot grow back. The axon eventually degenerates, and the cell body of the neuron may die.

The brain can adapt well to the loss of some neurons, and permanent disability may not occur for many years. However, more than 50% of patients with MS eventually enter a stage of progressive deterioration, called secondary progressive MS (SPMS). In this stage, the disease no longer responds well to disease-modifying drugs, and patients’ disabilities steadily worsen. The destruction of neurons from early in the natural course of MS suggests that the progressive disabilities of SPMS might be the result of an accumulated neuronal loss that eventually overwhelms the brain’s compensatory abilities.*

*Sections taken from Trapp, B. (2007). Nerve Fibers are Severed by Inflammation in MS Lesions, Leading to Permanent Disabilities. Multiple Sclerosis Quarterly Report, 26(2), 6-10. Copyright 2007 by United Spinal Association. Reprinted with permission

Who has it?

It is thought that 100 thousand people in the UK - about 1 in 600 - have been diagnosed. MS affects more women than men (by a ratio of 3:2) with symptoms usually becoming apparent in young adults (between the ages of 20 and 40) even though a firm diagnosis might not be made for many years. The youngest known cases of MS are just five years old but it is relatively rare for children to be diagnosed, although this is increasing year on year.

We have web pages specifically about Paediatric Multiple Sclerosis Research and Paediatric Multiple Sclerosis on the website.

What causes it?

No one knows - despite vast amounts of research which is still going on. Various factors may trigger an inborn susceptibility to MS. Such factors may cause inappropriate activity of the immune system - the body's defence mechanism - causing the destruction of myelin, see above.

Factors associated with MS may be more likely to occur in Northern Europe, Canada, the Northern States of the USA, New Zealand and Tasmania since these are the places where the incidence of MS is highest. MS is not contagious - you cannot catch it from someone.

What problems does it cause?

As with most chronic illnesses, the problems are both physical and emotional. The severity and incidence of symptoms vary enormously from person to person and even from hour to hour.

Did you know?

One-third of people diagnosed with MS are still working, walking & functioning relatively normally 25-30 years following their diagnosis