MS can affect any part of the central nervous system (the brain and spinal cord), damaging the protective layer around nerve fibres (called ‘myelin’), or the fibres themselves. This can mean messages get delayed, disrupted or stopped altogether.

Messages going to the brain (input messages) and messages leaving the brain (output messages) can both be affected, so the information the brain receives and the replies it sends back out can be late, incomplete or misleading. MS damage can also disrupt the messages being passed inside the brain, affecting how the brain processes balance information.  

Some symptoms of MS can also have a knock-on effect on balance. For example, tremor or muscle spasms can mean that an output message is disrupted: the brain processes the information correctly, but the muscle does not respond in the way it was intended. If balance is being affected by other symptoms, such as tremor, you may notice that your balance also gets better and worse as these other symptoms come and go.  

Vision – Not everyone with MS has problems with their eyes, but visual disturbances are a relatively common symptom in MS. Temporary double vision (or ‘diplopia’), for example, affects probably around a third of all people with MS at some time or other. Other disturbances can include blurring, or flashes of colours or light. Sometimes, stationary objects can appear to flicker or jump about.

These kind of changes can give confusing information to the brain when it tries to work out how the body is moving relative to the world around it. On their own, visual problems are not usually enough to upset someone’s balance, but together with other input messages, they may have an impact.

Obvious visual problems are often only temporary, during an attack of optic neuritis, for example, or sometimes during or shortly after exercise. More subtle changes may last longer which, even if they are not a problem in themselves, might affect balance through the misleading messages they send to the brain.

Sensory changes – Another common symptom with MS is changes in sensation, such as numbness or tingling, which can come and go and change over time.

These symptoms appear when MS damage in the brain or spinal cord delays, distorts or completely stops information coming from sensors in the skin, muscles or joints. As well as causing these unusual sensations, the brain may not be receiving the accurate information it needs for proper balance.

The inner ear – The inner ear constantly updates the brain about the angle and position of the head. If MS damages the message pathways from the inner ear area, confusing or missing signals can add to balance problems. If you experience ‘vertigo’ – spinning or falling sensations – this can be a sign
that messages from the inner ear are involved.
 

The brain can compensate for a certain amount of damage in different parts of the balance system. Even if input messages are disrupted there may be no obvious signs of balance problems. But if damage is more widespread, the effects can become noticeable, as the brain’s limits of compensation are reached.

The brain also appears to be better at dealing with missing information than with incorrect or misleading information. If MS distorts or delays input messages, the brain still responds as if the information is accurate. By responding to inaccurate information, the brain’s response can actually make balance worse, rather than better.

MS can also disrupt the messages going to and fro inside the brain. Almost every part of the brain is involved in balance in some way or another, but one area particularly associated with the process is the ‘cerebellum’. If MS causes damage to this area, the brain may be less able to compensate for missing or incorrect messages, or may send out misleading responses to the muscles as the body tries to balance.

MS damage to the cerebellum or to the ‘brainstem’ (at the back of the brain, where it joins the spinal cord) may also cause vertigo, sometimes accompanied by nausea. But vertigo and nausea can also be caused by changes in the inner ear, so it should not be assumed that MS is the cause.
 

MS can cause a wide range of symptoms that may also have an effect on balance, such as difficulties with coordination, tremor, muscle weakness, stiffness or spasms. MS varies greatly from person to person and not everyone experiences these symptoms, but as with visual and sensory changes, even small effects that are barely noticeable may have an impact on balance.

To react to changes in the body’s position, the brain needs to constantly instruct muscles to make tiny (and sometimes larger) adjustments. A weak or stiff muscle might not move to the desired position, or might get there too slowly. If this combines with misleading information about where the muscle is balance can be harder.