Fever of unknown origin
Fever of unknown origin (FUO) is defined as a sustained high body temperature of at least 101°F (38°C) lasting more than three weeks, with no identified cause after one week of investigation. The underlying reasons for FUO can be diverse and include rare infections, autoimmune diseases, some cancers, and adverse drug reactions, among others. Risk factors for developing an FUO encompass recent foreign travel, existing medical conditions such as cancer or autoimmune diseases, and certain medications.
Symptoms commonly associated with an FUO include fever, sweats, chills, and body aches, but these symptoms can arise from various underlying issues, not all of which are serious. Diagnosis typically involves a comprehensive evaluation by a healthcare provider, including a detailed medical history, physical examination, and various diagnostic tests like blood work and imaging studies to narrow down the possible causes. Treatment is only initiated once the underlying condition is identified, highlighting the importance of thorough investigation.
Preventive measures focus on maintaining overall health and adhering to public health recommendations, especially when traveling to areas with higher risks of certain infections. Understanding FUO can help individuals recognize when to seek medical attention and navigate the complexities of unexplained fevers.
Fever of unknown origin
Anatomy or system affected: All
Also known as: Pyrexia of unknown origin
Definition
A high body temperature without a clear cause is a fever of unknown origin, or FUO. An FUO is an intermittent temperature of a minimum 101° Fahrenheit (38-39° Celsius) and more than three weeks in duration. The FUO also is marked as such if a minimum of one week has passed in attempting to find its cause.
Causes
There are many rare causes of a high temperature. The following list includes a few of the uncommon causes: unusual infections, extrapulmonary tuberculosis, atypical tuberculosis, tropical diseases in temperate climates/latitudes (malaria, dengue fever, yellow fever), rare organisms (fungi, viruses, uncommon bacteria), obscure infections, prostatitis, sinusitis, hidden abscesses, collagen vascular (connective tissue, autoimmune) diseases, rheumatoid arthritis, systemic lupus erythematosus, inflammatory diseases, sarcoidosis, Crohn’s disease (regional ileitis), cancer, lymphoma (Hodgkin’s and non-Hodgkin’s), leukemia, kidney cancer, liver cancer, drug reactions, antibiotics, epilepsy medications, immunoglobulin, antipsychotic drugs (Thorazine, Haldol), antihistamines, hereditary metabolic diseases, hormone disturbances, hyperthyroidism, brain disorders that affect temperature regulation, tumors, and strokes.
Risk Factors
The factors that increase the chance of developing an FUO include foreign travel, especially to developing and tropical countries; current medications (both prescription and over-the-counter); cancer or brain tumor; collagen vascular disease (an autoimmune disorder of connective tissue); human immunodeficiency virus (HIV) infection; acquired immunodeficiency syndrome (AIDS); current or recent hospitalization; and similar problems in the patient’s family.
Symptoms
One should not assume these symptoms are caused by an FUO. A fever is a common indication of many problems. These problems can be both serious and trivial. One should consult a doctor if experiencing any of the following symptoms: elevated temperature by thermometer reading, sweats, chills, and widespread body aches.
Screening and Diagnosis
A doctor will ask about symptoms and medical history and will perform a physical exam. The patient can help the doctor by taking his or her own temperature several times a day. The doctor may refer the patient to a specialist.
The first efforts after the usual evaluation will be to narrow the possibilities. This is done by examining the circumstances under which the fever began. The doctor will ask questions about traveling abroad, hospitalization, any damage to the immune system (for example, by AIDS), and current medications.
Many different tests may be indicated at some point. These tests include exhaustive studies of blood, urine,and all other bodily products; exhaustive imaging studies, such as X rays, computed tomography (CT) and magnetic resonance imaging (MRI) scans, and ultrasound examinations; nuclear medicine studies; endoscopies (lungs, stomach and intestines, sinuses); and biopsies (samples taken by knife or needle) of suspect tissues.
Treatment and Therapy
There is no treatment for an FUO until the underlying disease is identified. When the fever’s cause is discovered, treatment will follow.
Prevention and Outcomes
There are many causes for an FUO. Prevention includes everything one does to stay healthy. One should take all preventive measures recommended by public health departments when traveling to developing countries or countries in tropical regions.
Bibliography
Amin, K., and C. A. Kauffman. “Problem Infections in Primary Care: Fever of Unknown Origin—A Strategic Approach to this Diagnostic Dilemma.” Postgraduate Medicine 114, no. 3 (September, 2003).
Beers, M. H., and R. Berkow. “Biology of Infectious Disease.” In The Merck Manual Home Health Handbook, edited by Robert S. Porter et al. 3d ed. Whitehouse Station, N.J.: Merck Research Laboratories, 2009.
Gelfand, J. A., and M. V. Callahan. “Fever of Unknown Origin.” In Harrison’s Principles of Internal Medicine, edited by Anthony Fauci et al. 17th ed. New York: McGraw-Hill, 2008.
Roth, A. R., and G. M. Basello. “Approach to the Adult Patient with Fever of Unknown Origin.” American Family Physician 68 (2003): 2223-2229. Available at http://www.aafp.org/afp/20031201/2223.html.
Torpy, J. “Fever in Infants.” Journal of the American Medical Association 291 (2004): 1284.