Fatigue is the seventh most common complaint in primary care. It can be the presenting symptom of almost any disease. Thorough history and physical examination will establish a diagnosis in about 85% of patients. If, in addition to experiencing fatigue, the patient complains of localizing symptoms such as abdominal pain or hemoptysis, the diagnosis is easier. Specific attention can then be focused on abdominal or chest causes, respectively. If the patient’s only complaint is fatigue, the diagnosis is more difficult.
Fatigue is often confused (by patients and doctors alike) with excessive daytime sleepiness. Fatigue is more likely to be called weariness, weakness, and depleted energy, whereas excessive daytime sleepiness may be called drowsiness, decreased alertness, and sleep propensity (“I can always go to sleep”). In fact, in one study of patients with obstructive sleep apnea, the patients usually complained of fatigue, tiredness, and lack of energy rather than sleepiness.
Fatigue can be categorized as acute, chronic, or physiologic. Acute fatigue is most often a prodrome or sequela of an acute viral or bacterial infectious process. Heart failure and anemia may also manifest as a sudden onset of fatigue.
Chronic fatigue (of weeks’ to months’ duration) can be caused by depression; chronic anxiety or stress; chronic infection, especially infectious mononucleosis, hepatitis, or tuberculosis; cancer; rheumatoid arthritis, fibromyalgia, and other rheumatologic disorders; heart failure; sleep apnea; serum electrolyte abnormalities (hyponatremia, hypokalemia, hypercalcemia); chronic lung disease; or anemia. Prescribed and over-the-counter drugs are common and frequently unrecognized causes of chronic fatigue, especially in patients older than 45 years. These drugs include antihistamines, tranquilizers, psychotropics, hypnotics, and antihypertensives (particularly reserpine, methyldopa, clonidine, and beta blockers).
Patients with physiologic fatigue usually recognize the cause of their fatigue and usually do not consult a physician about it. Physiologic fatigue can result from overwork (either physical or mental) and insufficient or poor-quality sleep, which may be caused by depression, caffeine, drugs, alcohol, or chronic pain.
In about 50% of patients who present with fatigue, the cause is functional (depression, anxiety, or a somatoform disorder); in the other 50% an organic cause exists. The physician must recognize that multiple causes of fatigue may be present. For example, a patient who complains of fatigue may demonstrate the signs and symptoms of depression and may also have hepatitis, infectious mononucleosis, or bronchogenic carcinoma.
Depression as a cause of fatigue is not a diagnosis of exclusion. Innumerable diagnostic tests to rule out all possible organic causes should not be performed before the diagnosis of depression is made. Instead, if thorough history and physical examination do not reveal clues to an organic cause but do uncover symptoms of depression, depression is the probable cause of the fatigue.
Fatigue is an uncommon complaint in children and young adults. When it is the presenting symptom, it is usually caused by a prodrome or sequela of an acute infectious process. Chronic fatigue in adolescents is most often related to infectious mononucleosis, hepatitis, substance abuse, depression, and/or chronic anxiety.
Depression in children seldom manifests as lowered mood or fatigue; instead, the children present with somatic complaints such as headache and acting out. Depression often manifests in children as hyperactivity, withdrawal, eating problems, school troubles, sleep disturbances, or vague physical complaints. When fatigue is associated with acting-out behavior (e.g., substance abuse, sexual misconduct) in adolescents, depression may be the underlying culprit. Illnesses such as cancer, chronic lung disease, heart disease, and leukemias are uncommon in children and adolescents.
As in younger patients, the most common cause of acute fatigue in adults is infection, followed by depression and anxiety. The incidence of fatigue has been reported to be higher in women than men. Life events such as childbirth and menopause may be responsible, although more women than men are diagnosed with depression as causing their fatigue.
In adult patients, particularly the elderly, serious organic illnesses, such as circulatory and pulmonary diseases, anemia, cancer, and endocrine abnormalities, are more likely to manifest as fatigue. In elderly patients, the chief complaint of masked hyperthyroidism may be fatigue. Patients with this condition do not necessarily show tachycardia, tremors, and other classic signs of hyperthyroidism. Weakness may be caused by diuretic-induced hypokalemia, psychotropic agents, alcoholism, and neuropathies. Sleep apnea, which is more common in obese patients and patients who snore, may lead the patient to complain of fatigue, not sleepiness.
Because fatigue is such a common symptom of depression in adults, the physician must recognize that the signs and symptoms of depression vary not only with age but also with gender and socioeconomic status (Table 14-1). Men more often demonstrate depression as guilt, feelings of helplessness, pessimism, and depressed moods. Early signs of depression in women include headache, insomnia, and withdrawal from social activities. Depressed patients of lower socioeconomic class are likely to have depressed moods, feelings of guilt, hopelessness, and dissatisfaction, and crying spells. They may complain of palpitations, loss of appetite, early awakening, and headaches. Depressed middle class patients state that they feel sad or blue, guilty, helpless, lonely, or anxious. They may complain of crying spells, initial insomnia, early awakening, loss of appetite, headache, and decreased libido. Patients of the upper socioeconomic class more often complain of fatigue, insomnia, anxiety and tension, dissatisfaction, and decreased interest in work and social life.