By Birgitta Johansson and Lars Rönnbäck
Fatigue after traumatic brain injury (TBI) is common, but often overlooked. But for people fighting their fatigue after brain injury day after day, fatigue is a major problem. This post-injury mental fatigue is characterized by limited energy reserves to accomplish ordinary daily activities. Persons who have not experienced this extreme exhaustion which may appear suddenly, and without previous warning during mental activity, do not understand the problem. This is especially difficult to understand as the fatigue may appear even after seemingly trivial mental activities which, for uninjured persons, are regarded as relaxing and pleasant, as reading a book or having a conversation with friends. A normal, well-functioning, brain performs mental activities simultaneously throughout the day, but after a brain injury, it takes greater energy levels to deal with cognitive and emotional situations.
In this chapter, we highlight mental fatigue after TBI. In the case of long-lasting mental fatigue, it could be the only factor that keeps people from returning to the full range of activities that they pursued prior to their injury with work, studies and social activities. We describe mental fatigue and suggest diagnostic criteria and we also give a theoretical explanation for this. At the end of the chapter, we discuss treatment strategies and give some examples of possible therapeutic alternatives which may alleviate the mental fatigue.
Normally, the brain works in an energy-efficient manner and prominent energy reserves are present. This is due to well-functioning ion channel and amino acid transport systems and other effective physiological processes. After brain injury, some of these systems are down-regulated, and when mental energy requirements are high the physiological processes do not function to their full capacity; these cease to function efficiently with a resultant energy loss. This may be an explanation as to why the mental fatigue appears.
1.1. When does mental fatigue occur?
Fatigue is one of the most important long-lasting symptoms following TBI, and is most severe immediately after head injury. However it is difficult to arrive at any clear figure as to how common fatigue or, in particular, mental fatigue is. The reason for this is that different results have been obtained, and these are attributable to differences in definitions and differences in the methodology in the various studies. In follow-up studies, the frequency of prolonged fatigue varies from 16 up to 73 % [4–6]. There is no correlation between persistent fatigue and severity of the primary injury, age of the person at injury or time since injury [7, 8]. For those suffering from fatigue 3 months after the accident the fatigue remained relatively stable during longer periods . In particular, for those subjects who were suffering from the syndrome one year after the accident improvement in the fatigue was limited .
In the above reports, fatigue is discussed in terms of a single construct, i.e. not differentiated between the physical or mental aspects. In this chapter, we consider mental fatigue as a separate construct and we discuss its relationship to cognitive and emotional symptoms.
1.2. Mental fatigue is not a separate diagnostic entity
Mental fatigue is not an illness, rather it represents a mental sequel, probably due to a disturbance of higher brain functions, either physical or psychological in origin. It is included in, and defined within the diagnoses Mild cognitive impairment (F06.7), Neurasthenia (F48.0) and Posttraumatic brain syndrome (F07.2) .
1.3. Typical characteristics of mental fatigue
A typical characteristic of pathological mental fatigue after TBI is that the mental exhaustion becomes pronounced during sensory stimulation or when cognitive tasks are performed for extended periods without breaks. There is a drain of mental energy upon mental activity in situations in which there is an invasion of the senses with an overload of impressions, and in noisy and hectic environments. The person feels that their brain is overloaded after a tiny load. Another typical feature is a disproportionally long recovery time needed to restore the mental energy levels after being mentally exhausted. The mental fatigue is also dependent on the total activity level as well as the nature of the demands of daily activities. Fatigue often fluctuates during the day depending on the activities carried out. Thus, this fatigue is a dynamic process with variations in the mental energy level. The fatigue can appear very rapidly and, when it does, it is not possible for the affected person to continue the ongoing activity. Common associated symptoms include: impaired memory and concentration capacity, slowness of thinking, irritability, tearfulness, sound and light sensitivity, sensitivity to stress, sleep problems, lack of initiative and headache .
For many persons, this mental fatigue is the dominating factor which limits the person’s ability to lead a normal life with work and social activities. For most people, fatigue subsides after a period of time while, for others, this pathological fatigue persists for several months or years even after the brain injury has healed. Interestingly, however is that as many as 30% of family or friends interpreted fatigue as laziness .
Theories as to the mechanisms accounting for mental fatigue including our own theory, suggest that cognitive activities require more resources and are more energy-demanding after brain injury than usual [13, 14]. Thus, more extensive neural circuits are used in TBI victims compared to controls during a given mental activity . This indicates an increased cerebral effort after brain injury.
Therapist Luann Jacobs describes mild TBI and the lack of energy and lack of endurance that many can experience. As they are able to do what is normal and what appears normal, they run the risk that their symptoms will be misunderstood .
“Mild brain injury is a real misnomer, as it conveys the idea that nothing much is a problem when quite the opposite is more often true. It is called “mild” because, in fact, the mildly brain injured can walk, talk, eat and dress independently, often times drive a car, shop, cook, go to school, or even work.
What the term fails to account for is the inherent limits of how often, for how long (endurance), and the all-important, how consistently (e.g., every day, once a week) these activities can be performed. Even more elusive is the concept of how many of these daily activities can be done sequentially in a given day as is normal in the lives of people who are not brain injured.
The fatigue they feel defies description, going far beyond and far deeper than anything a non-brain-injured person would consider profound exhaustion.”
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