Fatigue is one of the most disabling symptoms pwMS suffer from. In over 50% of pwMS fatigue is the one symptom they would like to get rid of most. MS-related fatigue has several underlying mechanisms. For a short discussion on the major mechanisms…….
(2) Another cause of fatigue is exercise related conduction block. This is when pwMS notice their legs getting weaker with exercise. We think this is due to demyelinated, or remyelinated axons, failing to conduct electrical impulses when they become exhausted. Exercise-induced fatigue is probably the same as temperature-related fatigue; a rise in body temperature also causes vulnerable axons to block and stop conducting. To deal with this type of fatigue we need therapies to promote remyelination and to increase conduction. These types of fatigue are treated by rest, cooling and possibly drugs such as fampridine that improve conduction. At the heart of this type of fatigue is localised EF (energy failure).
(3) The other cause of fatigue is neural plasticity. When the brain is damaged by MS other areas are co-opted to help take over, or supplement, the function of the damaged area. In other words, it takes more brain power to complete the same task that normal people do. This type of fatigue usually manifests as mental fatigue and is why pwMS have difficulty concentrating for prolonged periods of time. At present we have no specific treatment for this type of fatigue, but some patients find amantadine and modafinil helpful. In short, preventing the loss of brain power, or damage, in the first place should prevent this type of fatigue.
(4) Fatigue can also be related to so-called co-morbidities, or other diseases, that are related to MS. The big co-morbidities that cause fatigue that need to be screened for are:
- Infection; we all get tired when we have infections; it triggers sickness behaviour
- An underactive thyroid gland or hypothyroidism; this is commoner in pwMS
- Poor sleep hygiene and/or sleep disorders; if you are not sleeping well you feel tired in the morning
- Obesity; when you are overweight it takes more energy to perform physical tasks
- Depression and anxiety; fatigue is a common symptom of depression and anxiety
- Side effects of drugs; in particular drugs that cause sedation and from DMTs. Anticholinergics and anti-spasticity drugs are sedating and blunt cognition and may worsen MS-related fatigue. Specific side effects, for example, the flu-like side effects from interferon-beta may make fatigue worse.
- Deconditioning; deconditioning is simply the term we use for being unfit. If you are unfit, performing a demanding physical task makes you tired. Deconditioning is treated with exercise, which paradoxically can reduce fatigue.
- Poor nutrition; some pwMS are anorexic and eat very poorly and hence have little energy as a result of this. Although this is quite rare I look after a few pwMS with this problem. Similarly, overnutrition may have the same effect. Some of the hormones your gut produce cause you to feel tired and want to sleep; i.e. the so-called siesta effect. Reducing the size of your meals and changing your eating behaviour may improve post-prandial (after eating fatigue). I have a few patients who avoid eating lunch for this reason.
It is apparent from this discussion that fatigue in MS is more complex than you realise and needs a systematic approach to be treated and managed correctly. So be careful, or at least wary, when your neurologist simply wants to reach for the prescription pad to get you out of the consultation room. Like other MS-related problems, a holistic and systematic approach is needed to manage and treat MS-related fatigue correctly.
The following is a summary of the results of an old blog survey on the causes of fatigue.