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Fever of Unknown Origin

What Is Fever of Unknown Origin?

Fever of unknown origin (FUO), as its name says, is a high temperature without any known cause after diagnostic tests have been done.

What Causes FUO?

Three major causes are infections, tumors, and collagen vascular diseases. Collagen-vascular diseases include systemic lupus, rheumatoid arthritis, and scleroderma. They’re caused by the body’s immune (infection-fighting) system attacking its own organs.

Infections, the most common cause, include endocarditis (infection of the heart’s lining or valves), tuberculosis, abscesses, and viral infections such as cytomegalovirus infection. Tumors, the second most common cause, include Hodgkin’s and non- Hodgkin’s lymphomas. Other tumors are leukemia, multiple myeloma, and renal, liver, colon, and breast cancers. The most common collagen-vascular disease in young people is juvenile rheumatoid arthritis. In older people, it’s inflammation of the temporal artery, found at the temple region of the head.

Other rare causes of FUO are drugs such as antibiotics, antihistamines, antiseizure drugs, antiinflammatory drugs, and medicines used for acid reflux and peptic ulcers.

What Are the Symptoms of FUO?

The medical definition describes the symptom: a temperature of 101° F (38.3° C) for more than 3 weeks and no diagnosis after 1 week of evaluation.

How Is FUO Diagnosed?

As part of the evaluation, the health care provider will take a detailed history, do a physical examination, and order blood tests.

If the diagnosis remains unclear, the health care provider may order imaging studies, such as x-rays and computed tomography (CT) of the chest, abdomen (belly), and pelvis.

If endocarditis may be the cause, echocardiography (an ultrasound test using sound waves to take pictures of the heart) will be done.

How Is FUO Treated?

The disease causing the fever must be treated. A doctor who specializes in infections will help with diagnosis, evaluation, and treatment of infectious diseases. Antibiotics will be given for infections. If a tumor is found, an oncologist (a doctor specializing in cancer treatment) will be involved. For a collagenvascular disease, a rheumatologist (a doctor specializing in joint and collagen-vascular diseases) will help.

DOs and DON’Ts in Managing FUO:

  • DO remember that your health care provider won’t usually start using medicines without making a diagnosis. If the FUO remains undiagnosed, your health care provider may just watch for more symptoms.
  • DO report any new symptoms if you are being evaluated for FUO.
  • DO call your health care provider if you have a longlasting fever (101° F or higher).
  • DO call your health care provider if you have symptoms that may help make the diagnosis (e.g., cough, sputum production, shortness of breath, abdominal pain, diarrhea, bloody stools, muscle aches, joint aches, joint swelling, bone pain, or burning with urination).
  • DON’T get frustrated. FUO may be very hard to diagnose. About 5% to 15% of cases don’t have a diagnosis.
  • DON’T self-medicate. Follow the instructions of your health care provider and specialists.
  • DON’T forget that infection is the main cause of FUO. Common infections include urinary tract infections, pneumonia, tuberculosis, endocarditis, osteomyelitis (infection of the bone), tick-borne diseases (e.g., Lyme disease), gonorrhea, syphilis, herpes, HIV, AIDS, and abdominal abscesses.
FOR MORE INFORMATION

Contact the following sources:

  • American Academy of Family Physicians
    Tel: (800) 274-2237
    Website: http://www.aafp.org
  • American Medical Association
    Tel: (312) 464-5000, (800) 621-8335
    Website: http://www.ama-assn.org

Copyright © 2016 by Saunders, an imprint of Elsevier, Inc.

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