Many people go to the doctor because they feel tired all the time. Many of these patients are suffering from major depression. These depressed patients often feel better if they get more exercise. However, some patients feel tired because they are teetering on the edge of physical collapse because of some serious circulatory, metabolic, or neurologic disorder. If these seriously ill people try to exercise more, they may end up in big trouble. So it is important for doctors to make the correct diagnosis in these cases. Otherwise, the doctor may offer advice that does more harm than good.
According to the dictionary, fatigue is extreme tiredness, typically resulting from mental or physical exertion or illness. In other words, fatigue is nature’s way of telling you to rest. However, a person may feel fatigue for many different reasons. As psychologist Doug Lisle explained in his book The Pleasure Trap, all animals must balance three conflicting motivations: to feel pleasure, to avoid pain, and to conserve energy. So besides deciding whether an activity is pleasurable or painful, animals must also predict whether a pleasure is worth the energy they would have to expend to obtain it, and whether a pain would be so bad that the effort to avoid the pain would be worthwhile. This estimation that some effort would be either unproductive or dangerous can produce a sensation that is felt as fatigue.
Depression involves a problem with the brain’s ability to predict and feel pleasure. For this reason, the depressed person’s brain concludes that many kinds of physical and mental efforts would not be worthwhile. As a result, depressed people often feel fatigue, even if they are nowhere near their physical limits. (In contrast, people with mania often run themselves into a state of physical exhaustion.) When nondepressed people are approaching their physical limits, their brain warns them that further effort would be dangerous. This warning is also felt as fatigue, even if the person’s activity level is abnormally low. People who push themselves despite this warning can make themselves much sicker. This result is called post-exertional malaise, or the push-crash phenomenon. People who are this sick have a low health-related quality of life. As a result, they may look and feel depressed, which complicates the diagnosis.
Do not assume that someone can exercise his or her way out of a case of a chronic fatiguing illness. Many of these people have an underlying disorder that must be found and corrected. In the meantime, the people may have to avoid exercise, so that they can use their limited supply of energy to do the things that are most important to them.
Many of the problems that cause disabling fatigue fall into two basic, overlapping categories: problems with energy metabolism (cellular respiration) and problems with standing or sitting up (orthostasis).
Many different kinds of problems can interfere with cellular respiration. Lung diseases can limit the flow of oxygen into the bloodstream. Anemia limits the blood’s ability to pick up the oxygen and carry it to tissue. Circulatory disease limits the body’s ability to deliver oxygenated blood to tissue. Nutritional deficiencies or damage to the cells’ mitochondria can interfere with the body’s ability to use oxygen to burn fuel to release energy.
In other words, chronic fatigue can result from a wide variety of serious diseases, many of which are so rare that doctors do not routinely test for them or even know about them. Each of these rare diseases affects only a few people. Yet together, these rare but serious fatiguing illnesses could account for a large number of people, most of whose illnesses never get a proper diagnosis.
Some of these rare problems can be caught if the doctor listens and looks: takes a careful history and does a careful physical examination. For example, to catch cases of spinal fluid leak, doctors must look for patients who have a connective tissue disorder (abnormally tall or abnormally flexible) or a history of spinal injury/surgery or lumbar puncture. They must also listen to the patient’s complaints. Patients with a spinal fluid leak will typically say that they feel better in the morning or after prolonged bed rest but worse in the afternoon or evening or after prolonged sitting or standing. An ordinary MRI might not reveal the leak. Instead, the patient may need magnetic resonance myelography. Yet if the leak is found and patched, the patient can get well.
Low blood volume (hypovolemia) can easily be mistaken for an anxiety disorder. These patients are pale because of poor circulation. The extra norepinephrine that their adrenal glands release to compensate for the shortage of blood can cause tremor and mood disturbance. Their pulse tends to be rapid and weak. In addition to fatigue, hypovolemic patients may complain of dizziness or fainting and an inability to see when they stand up. Yet the results of their complete blood count may be perfectly normal. However, the complete blood count only tells you whether the blood is good. It does not tell you how much blood the patient has. To test for low blood volume, start with a poor-man’s tilt table test: take the pulse and pressure while the patient is lying down, sitting, and then standing. If the pulse goes up a lot or the pulse pressure (systolic minus diastolic pressure) goes down while the patient is standing, the patient probably has low blood volume.
Remember that many vague symptoms, including fatigue, can result from food allergy or intolerances. Doctors can solve many of these problems just by giving the patient a simple handout with instructions on how to follow an elimination diet.
Many patients who are on the edge of physical collapse are mistakenly thought to be suffering from a primarily psychiatric problem. Yet if the patient is on the edge of physical collapse, misguided psychotherapy and the pressure to exercise can do a great deal of harm. If the underlying physical problem cannot be resolved, the patient needs coping skills for living with the disability, as well as help in getting others to understand and accept his or her level of disability.