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In this chapter, we consider the clinically related phenomena of lassitude, fatigue, nervousness, irritability, anxiety, and depression. These complaints form the core of a group of "symptom-based" disorders that are a large part of medical practice. Although more abstruse than paralysis, sensory loss, seizures, or aphasia, they are no less important, if for no other reason than their frequency. In an audit of one neurologic practice, anxiety and depressive reactions were the main diagnosis in 20 percent of patients, second only to the symptom of headache (Digon et al). Similarly, in two primary care clinics in Boston and Houston, fatigue was the prominent complaint in 21 and 24 percent of patients, respectively. Some of these symptoms represent only slight aberrations of function or a heightening or exaggeration of normal reactions to environmental stress or to medical and neurologic diseases; others are integral features of the diseases themselves; and still others represent disturbances of neuropsychiatric function that are components of the diseases described in Chaps. 51, 52, and 53 on psychiatry.


Of the symptoms considered in this chapter, lassitude and fatigue are the most frequent, and the most vague. Fatigue refers to the universally familiar state of weariness or exhaustion resulting from physical or mental exertion. Lassitude has much the same meaning, although it connotes more of an inability or disinclination to be active, physically or mentally. More than half of all patients entering a general hospital register a complaint of fatigability or admit to it when questioned. During World War I, fatigue was such a prominent symptom in combat personnel as to be given a separate place in medical nosology, namely combat fatigue, a term that came to be applied to practically all acute psychiatric disorders occurring on the battlefield. In subsequent wars, it has become a key element of the posttraumatic stress disorders related to exposure to highly stressful circumstances. The common clinical antecedents and accompaniments of fatigue, its significance, and its physiologic and psychologic bases will be better understood if we first consider the effects of fatigue on the normal individual.


Effects of Fatigue on the Normal Person


Fatigue has three basic meanings: (1) biochemical and physiologic changes in muscles and a reduced capacity to generate force manifest as weakness, or asthenia; (2) a disorder in behavior, taking the form of a reduced output of work (work decrement) or a lack of endurance; and (3) a subjective feeling of tiredness and discomfort.


The decreased productivity and capacity for work, which is a direct consequence of fatigue, has been investigated by industrial psychologists. Their findings clearly demonstrate the importance of motivational factors on work output, whether the effort is of physical or mental type. Quite striking are individual constitutional differences in energy, which vary greatly, just as do differences in temperament. What should be emphasized is that in the majority of persons complaining of fatigue, ...

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