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Medical Author:

Charles Patrick Davis, MD, PhD

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Medical Editor:

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Drug fever

A fever that occurs after starting a new medication, without another source, may be a drug fever. The fever can occur at any time after starting the drug and should go away after the drug is stopped. Some drugs that have been associated with fever include beta-lactam antibiotics, procainamide (Procanbid), isoniazid, alpha-methyldopa, quinidine (Quinaglute Dura-Tabs), and diphenylhydantoin.

• An immediate fever may be caused by an allergic response to the medication or a preservative in the medication.

Blood clot fever

Occasionally a blood clot can develop in a person's leg and cause swelling and pain in the calf. Part of this clot may break off and travel to the lungs (pulmonary embolus). This may cause chest pain and trouble breathing. In either case, a person may develop a fever because of inflammation in the blood vessels. A person with any of these symptoms should go to the hospital.

Tumor fever

Cancer can cause fever in a variety of ways. Sometimes the tumor makes pyrogens, chemicals which cause a fever on their own. Some tumors may become infected. Tumors in the brain may prevent the hypothalamus (the body's thermostat) from properly regulating the body temperature. Many of the medications that a cancer patient takes can cause a fever. Finally, immune systems in cancer patients may be weakened, which makes them prone to various infections.

Environmental fever

Occasionally a very high body temperature can be reached when the body becomes overheated. This condition is called hyperthermia. This often occurs with strenuous exercise or when the body is exposed to hot or humid weather. Certain drugs that alter a person's behavior may prevent that person from taking shelter from the heat. People with hyperthermia may be confused, lethargic, or even comatose. They may have an extremely high temperature and may not be able to sweat. Hyperthermia is treated differently than other causes of fever; it is a medical emergency. The affected person must be cooled immediately.

Special medical conditions

Many people have medical illnesses that prevent their immune system (defense system) from working normally. This may make it easier for a fever-causing infection to invade their body. Depending on the illness, it may be difficult to find the source of the fever. A fever in a person with limited ability to fight off infection can be very dangerous. The collagen vascular diseases and autoimmune diseases (for example, systemic lupus erythematosus, rheumatoid arthritis, polyarteritis nodosa) may be associated with fever. Many diseases of the immune system produce fever, because of inflammation.

Causes of a weakened immune system

• Cancer
• Cancer treatments
• Organ transplant immunosuppressive medication
• Steroid therapy for a long time
• HIV
• Age older than 65
• Absence of the spleen (after surgical removal of the spleen)
• Sarcoidosis (a condition characterized by an unusual form of inflammation, leading to the formation of so-called granulomas, that may occur anywhere in the body)
• Lupus
• Malnutrition
• Diabetes
• Heavy alcohol or drug use

Any person with one of these illnesses or conditions and a fever should see a doctor or go to a hospital's emergency department quickly. It is important for the proper treatment to be started right away. Quick action may save the person's life.

Another medical condition that involves fever is unusual as the cause is unknown or unexplained (although the cause may be discovered at a later date). It is termed FUO (fever of unknown origin). FUOs are defined as a temperature greater than 101 F (38.3 C) on several occasions, with more than three weeks' duration of such febrile illness, and failure to reach a diagnosis despite intensive investigation, which some investigators consider to be one week of inpatient investigation. Eventually, FUOs are found to be caused by infections (30%-40%), cancers (20%-30%), collagen vascular diseases (10%-20%), and numerous miscellaneous diseases (15%-20%) such as abscess in organs, obscure parasitic infections, and occult cancers. Unfortunately, about 5%-15% of FUO cases defy diagnosis, despite expert evaluations and many tests.

Another special medical condition involves hypothalamus regulation. Neurotransmitters and hormones (for example, thyroid hormones) work through feedback mechanisms to help the hypothalamus function. If this delicate feedback balance is interrupted, the hypothalamus may malfunction in many ways, one of which is to raise core body temperature to fever levels. Thyroid storm (also termed thyrotoxicosis) is a medical emergency in which fevers reach about 105.8 F (41 C).

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