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Fatigue is probably the most common symptom of multiple sclerosis and the majority of people with MS (PwMS) experience it at some point in their disease course, often chronically and for the entire course of the disease.

Fatigue in multiple sclerosis can take two forms - mental and physical.

Mental fatigue can vary between mild and severely disabling and is usually exacerbated by exercise, increased bodily or ambient temperature (Uhthoff's symptom).

Mental fatigue usually follows a daily pattern and, in this respect, differs from the constant fatigue associated with depression. Many PwMS report that they feel fine during the first few hours of the day but, by afternoon or early evening, feel completely exhausted. Often a nap or a short period of rest will help them recover.

Fatigue in MS appears to be unrelated to disability status and many PwMS complain of fatigue even when all their other symptoms are mild or in complete remission.

Why PwMS get so tired is not very well understood. Sleep disturbance is cited as one possible explanation and PwMS are three times as likely to have disturbed sleep as the rest of the population. A number of factors contribute to this, including a reduction in sleep efficiency (demonstrated by polysomnographical studies), periodic involuntary leg movements and urinary urgency.

Attempts to correlate mental fatigue with the location of MRI lesions have revealed some rather weak correlations - for example, lesions in the frontal white matter and the deep white matter of the right insula. Lesions in the cerebellum and brainstem that cause involuntary nocturnal spasms are also implicated. Despite this, MRI lesion load and fatigue do not correlate very well.

Depression and fatigue also do not correlate very well in multiple sclerosis.

Physical fatigue can be easily induced in MS by a short walk or other physical activity. For some reason, also not fully understood, the efficiency of demyelinated nerves deteriorates very rapidly with use. Almost everyone whose physical functioning has been disturbed through MS finds that their ability to do things reduces as they do them.

A typical phenomenon is for a PwMS to set out on a short stroll walking reasonably well but as they continue their gait deteriorates or becomes impossible as physical fatigue sets in. Just lifting a foot to take the next step can be an enormous effort. If they push themselves beyond their limit they become completely exhausted and feel like they have run a marathon.

Mental fatigue is often associated with physical fatigue and all you want to do after physical exercise is to collapse on a bed and sleep.

Resting usually helps and many tasks can be completed if broken down into little bits with frequent rests in between. Recovery times vary, usually depending on how severe the disability is. Some people may be able to resume the activity within minutes, whereas others may need hours.

As with mental fatigue and most other MS symptoms, heat makes physical fatigue worse.

The received wisdom is to discover your limits and not to push yourself beyond them or else you risk wiping yourself out for hours or days. It is important to keep up with what exercise one is capable of to prevent the muscles from atrophying and to keep the nerve pathways as operational as possible.

A number of methods of measuring fatigue in multiple sclerosis have been developed including the Fatigue Descriptive Scale (FDS).

Drug treatments for fatigue in multiple sclerosis include Amantadine, Modafinil, Pemoline, and Methylphenidate.

Fatigue links:
The symptoms of chronic fatigue syndrome are related to abnormal ion channel function

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