Types of Fatigue

Over 100 years ago William Osler, the father of internal medicine, divided fatigue into three types. The first is the lassitude and malaise associated with systemic illness such as tuberculosis, cancer, rheumatoid arthritis, etc. The second is the weakness associated with muscle and nerve disorders resulting from ordinary exertion. The last is a painful weariness – the cause of which often eludes investigation.

These categories provide a useful framework in attempting to diagnose the cause of an individual’s fatigue. Duration further categorizes the symptom. Most patients with prolonged, unexplained fatigue have the third type of fatigue described by Osler, a painful weariness.

Fatigue that is less than one-month in duration is often due to a passing virus, stress, or other causes that are difficult to define. The relatively brief nature of the problem eliminates the need for an intense medical investigation, and, unless the problem becomes recurrent, it can be dismissed as one of life’s minor problems.

Persistent, significant fatigue, however, is not a minor problem. Even a loss of 10% of a person’s vigor removes enthusiasm and joy from the day’s tasks. Fatigue pulls down the mood and makes everything an effort. Approximately 15% of the general population suffers from chronic fatigue, unrelieved by rest, lacking an adequate medical explanation.

Approximately 25% of patients visiting a medical doctor complain of fatigue. Less than half will be explained by a medical illness.

Fatigue caused by medical conditions has certain characteristics. A serious medical problem will occasionally present itself as unexplained fatigue before other symptoms become apparent but, inevitably, other symptoms will appear. For instance, a person with pancreatic cancer may first notice fatigue before the appearance of abdominal pain and the other symptoms of cancer occur. Therefore, the longer fatigue persists without other symptoms, the less likely a serious medical condition will serve as the eventual explanation.

Fatigue caused by a medical problem has other characteristics as well. Usually patients with typical, diagnosable, medical problems note that their energy is highest in the morning and slowly winds down over the course of the day as if the store of vigor slowly depletes. A nap may recharge the person.

Fatigue that remains unexplained usually has different characteristics. Many times, a person has a bimodal curve of energy, worse in the morning, improving with the day, fading in the afternoon, and, finally, getting a second wind at night. A nap can actually worsen things. Additionally, sleeping a long time can produce an overslept sensation.

Patients with less serious medical problems can, in certain circumstances, have fatigue with the absence of other symptoms, as is the case with hypothyroidism. Patients with low thyroid may notice tiredness before the other symptoms appear. These include dry skin, constipation, cold intolerance, etc. Likewise, a patient with anemia can feel tired before noticing other symptoms such as pale skin or obvious blood loss.

Causes of fatigue are often easy to figure out. Usually a visit to the doctor and a standard panel of blood tests provides a definite answer. If, after a thorough exam and appropriate blood tests, no answer is apparent, it is unlikely that a medical explanation will be found.