How Does MS Work?

The inflammation and demyelination seen in MS don’t go unchecked—the body fights back. As nerves become demyelinated, specialized cells (called oligodendrocytes) produce new myelin to repair the damage. This can partially restore nerve function, which may help to explain why symptoms go away during periods of remission.

However, patching up myelin isn’t an efficient process and early on in the disease, the repair work can fall behind, meaning that there is a slow accumulation of damage over time. When an axon (nerve fibre) accumulates so much damage that it becomes severed—when it can’t transmit any more information—this is called axonal transection.

At some point, the ongoing accumulation of nerve damage may signal the beginning of the secondary-progressive phase of MS—most people with relapsing-remitting MS will go on to develop secondary-progressive MS. During this phase, there are generally fewer relapses and less inflammatory activity, but the effects of the disease steadily increase because of ongoing axonal damage.

Many researchers now believe that progression of disability—moving from relapsing-remitting to secondary-progressive MS—occurs when nerve damage reaches a tipping point: a point at which countless small changes suddenly produce a big effect. It’s like the one snowflake too many that causes an avalanche. The time that it takes to reach this point varies widely, from a few years to over twenty years—it depends on the person. Why some people progress more rapidly than others isn’t entirely clear. Unfortunately, there’s no way to tell at the outset who will have an easier time of it and who will develop disabilities.

MS is an illness of uncertainty: What symptoms will occur? Will there be a relapse? Will I be able to do everything I want to do today? And perhaps the greatest of all the uncertainties is: Will I become disabled? This is one of the biggest worries for people living with MS.

But we do know, amid all the uncertainties, is that it’s crucial to do everything possible to slow down the disease process and avoid reaching the tipping point of nerve damage: once that threshold has been crossed, whatever functions that have been lost cannot be regained.

What is MS?