Several features are common to the psychiatric group with fatigue. Tests of peak muscle power on command, with the patient exerting full effort, reveal no weakness. The sense of fatigue may be worse in the morning. The fatigue is worsened by mild exertion and relates more to some activities than to others. Inquiry may disclose that the symptom was first experienced in temporal relation to a grief reaction, a surgical procedure, physical trauma such as an automobile accident, or a medical illness such as myocardial infarction. The feeling of fatigue interferes with both mental and physical activities; the patient is easily worried, is “full of complaints,” and finds it difficult to concentrate in attempting to solve a problem or to read a book, or in carrying on a complicated conversation. Also, sleep is disturbed, with a tendency to early morning waking, so that such persons are at their worst in the morning, both in spirit and in energy output. Their tendency is to improve as the day wears on, and they may even feel fairly normal by evening. Severe fatigue that causes the patient consistently to go to bed right after dinner and makes all mental activity effortful should suggest an associated depression. It may be difficult to decide whether the fatigue is a primary manifestation of the disease or secondary to a lack of interest.
Not unexpectedly, fatigue and intolerance of exercise (i.e., fatigue with even mild exertion) are prominent manifestations of certain muscle disease. The most prominent such disorder displaying fatigue and lack of muscular endurance is myasthenia gravis, in which progressively less power is developed with each muscle contraction. In addition to myasthenia gravis, the classes of myopathy in which weakness, inability to sustain effort, and excessive fatigue are notable include the muscular dystrophies, congenital myopathies, other disorders of neuromuscular transmission (Lambert-Eaton syndrome), toxic myopathies (e.g., from cholesterol-lowering drugs), some of the glycogen storage myopathies, and mitochondrial myopathies. One type of glycogen storage disease, McArdle phosphorylase deficiency, is exceptional in that fatigue and weakness are accompanied by pain and sometimes by cramps and contracture. Another such process, acid maltase deficiency, is at times associated with disproportionate weakness and fatigue of respiratory muscles, which leads to dyspnea and retention of carbon dioxide. The characteristics of these diseases are presented in the chapters on muscle disease. Further comments on muscular fatigue can be found in Chap. 45.
Fatigue of varying degree is also a regular feature of all diseases that are marked by denervation of muscle and loss of muscle fibers. Fatigue in these cases is a result of the excessive work imposed on the remaining intact muscle (overwork fatigue). This is most characteristic of amyotrophic lateral sclerosis and the postpolio syndrome, but it also occurs in patients as they are recovering from Guillain-Barré syndrome and in those with chronic polyneuropathy.
Not surprisingly, many neurologic diseases that are characterized by difficulty engaging the muscles (Parkinson disease is the main example). Muscles partially paralyzed by a stroke feel tired and may cause an overall fatigue state. The distinguished neuroanatomist A. Brodal gave an interesting account of his own stroke and its effects on muscle power. Fatigue is often a major complaint of patients with multiple sclerosis; its cause is unknown, although the effect of cytokines circulating in the cerebrospinal fluid has been postulated. The depression that follows stroke or myocardial infarction frequently presents with the complaint of fatigue rather than other signs of mood disorder. Inordinate fatigue is a common complaint among patients with postconcussive syndrome (see Chap. 34). These central fatigue states and their possible mechanisms, almost all speculative, have been discussed by Chaudhuri and Behan.