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In this chapter, we consider the clinically related phenomena of fatigue, nervousness, irritability, anxiety, and depression. These complaints form the core of a group of symptom-based disorders with normal neurologic findings that are ubiquitous in 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 a large neurologic practice, anxiety and depressive reactions were the main diagnosis in 20 percent of patients, second only to headache (Digon et al). The prevalence of fatigue was 25 percent in a survey of patients in general practices in Ireland (Cullen et al). Similarly, in primary care clinics in Boston and Houston, fatigue was the prominent complaint over 20 percent of patients. Some of these symptoms represent only slight aberrations of function or heightened normal reactions to environmental stress or to 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. 47 through 49 on psychiatric diseases as viewed through the perspective of neurology.
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Of the symptoms considered in this chapter, fatigue is 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 in some literature it connotes more of an inability or disinclination to be active, physically or mentally, a “weariness of spirit.” 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 in the past was applied to practically all acute psychiatric disorders occurring on the battlefield and now called posttraumatic stress disorder. The physiologic accompaniments of this particular military and related forms of fatigue were also extensively studied by prominent clinicians such as Paul Dudley White.
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Fatigue has three basic meanings as experienced in daily life: (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 or a lack of endurance; and (3) a subjective feeling of tiredness and the mental discomfort that is associated with such an unnatural state for the individual.
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The first of these is due to the disease of muscle, nerve, or neuromuscular junction and is addressed in appropriate chapters of the book. The decreased productivity and capacity for work, which is a direct consequence of fatigue, has been investigated by industrial psychologists and physiologists. Their findings demonstrate the importance of motivational factors on work output, whether the effort is of ...