Fatigue is one of the commonest symptoms of MS and one that can often cause major problems to people's lives.
The cause of fatigue in MS is not well understood. It is thought to result from a combination of factors, partly caused by MS itself (known as primary fatigue) and partly by other factors (secondary fatigue) that affect the person with MS more significantly than those without the condition.
Primary fatigue is thought to be a combination of slowed nerve messages from the brain and spinal cord and a build up of weakness in muscles due to lack of stimulation. The level of fatigue does not reflect the severity of someone's MS and people can experience fatigue that prevents them from working or which interrupts their daily life whilst having no other symptoms.
MS fatigue or 'lassitude' is very different from the tiredness or exhaustion that people without MS experience following strenuous exercise or a busy day at work. Fatigue is described as interfering with normal activity and being out of all proportion to any activity undertaken. It is characterised by the sudden loss of energy and the inability to continue an activity.
MS can also cause 'short-circuiting' or neuromuscular fatigue. This happens if nerve messages to muscles become confused when someone is performing repeated movements. Messages start to 'leak' into other nerve cells and it becomes harder for the brain to get instructions through. For example, the legs may become increasingly heavy and difficult to move when walking, or the arms may be affected when writing for a period of time.
Secondary fatigue is fatigue that results from another symptom or cause, rather than being caused by the condition directly. Factors that can add to fatigue include lack of sleep, low mood or depression, stress, inadequate diet, lack of exercise, infections or side effects of medication.
Heat can increase fatigue in MS and some people with MS find that symptoms get worse during spells of hot weather. This was first observed in the late nineteenth century, and for a time, one of the diagnostic tests for MS was to put the patient into a hot bath and observe if this made symptoms worse.
- More information from the MS Trust
- Living With Fatigue
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