Fatigue is complicated and multifactorial. It may be classified as:
Primary fatigue
Primary fatigue is apparently directly related to neurological damage, affecting one’s ability to activate or control muscle groups. It commonly affects walking.
This is where damage to the central nervous system directly contributes to physical disability and means that the person affected must increase their efforts to make desired movements, and this will be fatiguing.
In addition, damaged central nervous system circuitry can also give rise to spasticity and muscle stiffness.
Secondary fatigue
Secondary fatigue is related to a variety of problems caused by the disease, including: lack of sleep; having to use the toilet in the night due to bladder issues; altered mood; muscle weakness owing to the effects of reduced exercise; and muscle spasm or stiffness.
In some circumstances symptoms may arise for both primary and secondary reasons, for example where there is a raised core temperature during an infection, that may have an impact on nerve impulse conduction (primary) but also making the person feel unwell (secondary).
Increased temperature in the body caused for example by exercise or a change in the weather (Uhthoff’s phenomenon), is well known to exacerbate symptoms and would therefore be expected to increase the feeling of fatigue.
One possibility is that it is the inflammatory component of the disease itself that gives rise to the feeling of fatigue, some pwMS treated with Tysabri tell us that in addition to relapse cessation, their fatigue is also notably improved.
Neurologists are trying to find biomarkers, for example IL-1b, that are both raised during inflammation and that can be measured in saliva. They could then be used as a way of quantifying both ongoing immune activity and fatigue.
by Dr Mark Baker