Many fevers (defined as a body temperature higher than 99 degrees Fahrenheit or 37 degrees centigrade) are associated with infections or other causes that are easy to identify. As soon as the underlying cause is resolved, the temperature usually returns to normal.
In addition to infections, any disorder or injury that produces tissue damage or inflammation can cause a fever, including heart attacks, cancer, burns, and broken bones. In some instances, the cause is not readily apparent, and the fever may persist for days or even weeks, often on an intermittent basis. These chronic fevers are often referred to as fevers of unidentified origin, or FUO for short. Finding the underlying cause of such fevers often requires considerable medical detective work. Frequently, however, the fever is accompanied by other symptoms that provide important clues to the underlying cause.
Causes of intermittent or chronic fevers
An abscess is a walled off, puss-filled pocket of bacterial infection that forms somewhere in the body. Some abscesses, such as the boils that form just under the skin, are familiar and readily apparent. Less familiar are abscesses that develop in internal organs, such as the lungs, brain, and liver. Antibiotics often fail to eradicate the underlying infection because the drugs may not penetrate the abscess wall. Such internal abscesses can produce a variety of symptoms, depending upon the affected organs. For example, a brain abscess can encroach on brain structures, producing symptoms similar to those of a tumor. Frequently, however, the major symptom is a chronic, low-grade fever.
In an autoimmune disease, the body's protective immune system goes awry and destroys normal body tissue as if it were an outside invader. Although there is no infection, the body often reacts as if there were. Thus, a chronic fever is a common symptom of many autoimmune diseases. There may also be inflammation in the joints or other organs that are under attack.
In rheumatoid arthritis, for example, there is often a chronic, low-grade fever as well as joint inflammation and pain. Lupus, another autoimmune rheumatic disorder, is also characterized by a chronic fever, although the other symptoms vary considerably according to the site of organ involvement.
Fever is a common result of inflammation, including inflammatory conditions affecting the heart and blood vessels. A serious heart infection called subacute bacterial endocarditis often produces a chronic low-grade fever. In this disease, bacteria invade the lining of the heart and heart valves. If untreated, the smoldering infection can destroy the heart valves, eventually leading to heart failure and death. Aortic inflammation (temporal or giant-cell arteritis) is an inflammation of the walls of the aorta, the body's largest artery. Initially, the major symptoms are a chronic, low-grade fever, malaise, weakness, and distorted or diminished vision.
Various inflammatory bowel disorders often produce chronic or intermittent low-grade fevers. In Crohn's disease (inflammation of the small and large intestines), fever, weight loss, and diarrhea are common early symptoms. Diverticulitis, an intestinal disease in which outpouches form in weakened segments of the colon, often produces a chronic fever along with abdominal pain and diarrhea alternating with constipation. Ulcerative colitis, a chronic inflammatory disorder affecting the colon, and enterocolitis, in which both the small intestine and colon are inflamed, also can cause chronic fever as well as GI symptoms.
Medication side effects
A number of medications can cause drug fever, an elevated temperature that is a side effect of treatment rather than a symptom of underlying disease. The most common causes of drug fever are antibiotics (especially sulfa drugs), psychotropic medications (especially barbiturates), antihistamines, and certain drugs used to lower high blood pressure.
This disease is characterized by the formation of nodules or masses called granulomas in various internal organs. The lungs and liver are the disease's most common targets; other organs that are often affected include the lymph nodes, salivary glands, eyes, heart, skin, and central nervous system. In addition to a chronic, low-grade fever, symptoms may include weight loss, joint pain, difficulty breathing, and enlarged lymph nodes.
The revved-up metabolism that characterizes an overactive thyroid gland (hyperthyroidism) sometimes produces chronic or intermittent fevers. Other symptoms may include palpitations, diarrhea, weight loss, nervousness, intolerance to heat, sweating, and bulging eyes.
Advice about intermittent or chronic fevers
- Any persistent, unexplained fever should be investigated by a doctor.
- A fever that develops a few days or even weeks after taking a medication may be an adverse side effect of the drug. Call a doctor as soon as possible and ask for guidance as to what medications should be avoided.