Fever

Fever (also known as pyrexia or controlled hyperthermia) is a common medical sign characterized by an elevation of temperature above the normal range of 36.5–37.5 °C (98–100 °F) due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.

As a person's temperature increases there is generally a feeling of cold despite an increasing body temperature. Once the new temperature is reached there is a feeling of warmth. A fever is one of the body's immune responses which attempts to neutralize a bacterial or viral infection. A fever can be caused by many different conditions ranging from benign to potentially serious. With the exception of high-grade fever, treatment is often not needed, however ibuprofen is effective at lowering the temperature.

Fever differs from uncontrolled hyperthermia, usually just referred to as hyperthermia, in that hyperthermia is an increase in body temperature over the body's thermoregulatory set-point, due to excessive heat production and/or insufficient thermoregulation.

Definition

A wide range for normal temperatures have been found. Fever is generally agreed to be present if:

• Temperature in the anus (rectum/rectal) is at or over 37.5–38.3 °C (100–101 °F)
• Temperature in the mouth (oral) is at or over 37.7 °C (99.9 °F)[8]
• Temperature under the arm (axillary) or in the ear (otic) is at or over 37.2 °C (99.0 °F)
• In healthy adult men and women the range for oral temperature is 33.2–38.2 °C (92–101 °F), for rectal it is 34.4–37.8 °C (94–100 °F), for tympanic membrane it is 35.4–37.8 °C (96–100 °F) and for axillary it is 35.5–37.0 °C (96–99 °F).

People develop higher temperatures with activities but this is not considered a fever as the set-point is normal. Elderly people have a decreased ability to generate body heat, so even a low-grade temperature may represent a serious underlying illness.

Types

The pattern of temperature changes may occasionally hint at the diagnosis:

• Intermittent fever: Elevated temperature is present only for some hours of the day and becomes normal for remaining hours, e.g. malaria, kala-azar, pyaemia, or septicemia. In malaria, there may be a fever with a periodicity of 24 hours (quotidian), 48 hours (tertian fever), or 72 hours (quartan fever, indicating Plasmodium malariae). These patterns may be less clear in travelers.
• Pel-Ebstein fever: A specific kind of fever associated with Hodgkin's lymphoma, being high for one week and low for the next week and so on. However, there is some debate as to whether this pattern truly exists.
• Continuous fever: Temperature remains above normal throughout the day and does not fluctuate more than 1 °C in 24 hours, e.g. lobar pneumonia, typhoid, urinary tract infection, brucellosis, or typhus. Typhoid fever may show a specific fever pattern, with a slow stepwise increase and a high plateau.
• Remittant fever: Temperature remains above normal throughout the day and fluctuates more than 1 °C in 24 hours, e.g. infective endocarditis.
• A neutropenic fever, also called febrile neutropenia, is a fever in the absence of normal immune system function. Because of the lack of infection-fighting neutrophils, a bacterial infection can spread rapidly and this fever is therefore usually considered a medical emergency. This kind of fever is more commonly seen in people receiving immune-suppressing chemotherapy than in apparently healthy people.

Febricula is a mild fever of short duration, of indefinite origin, and without any distinctive pathology.

Hyperpyrexia

Hyperpyrexia is a fever with an extreme elevation of body temperature greater than or equal to 41.5 °C (106.7 °F). Such a high temperature is considered a medical emergency as it may indicate a serious underlying condition or lead to significant side effects. The most common cause is a intracranial hemorrhage. Other possible causes include sepsis, Kawasaki syndrome, neuroleptic malignant syndrome, drug effects, serotonin syndrome, and thyroid storm. Well infections are the most common cause of fevers as the temperature rises other causes become more common. Infections commonly associated with hyperpyrexia include: roseola, rubeola and enteroviral infections. Immediate aggressive cooling to less than <38.9 °C (102.0 °F) has been found to improve survival. Hyperpyrexia differs from hyperthermia in that in hyperpyrexia the body's temperature regulation mechanism sets the body temperature above the normal temperature, then generates heat to achieve this temperature, while in hyperthermia the body temperature rises above its set point.

Hyperthermia

Hyperthermia occurs from a number of causes including heatstroke, neuroleptic malignant syndrome, malignant hyperthermia, stimulants such as amphetamines and cocaine,idiosyncratic drug reactions, and serotonin syndrome.

Signs and symptoms

A fever is usually accompanied by sickness behavior which consists of lethargy, depression, anorexia, sleepiness, hyperalgesia, and the inability to concentrate.

Differential diagnosis

Fever is a common symptom of many medical conditions:

• Infectious disease, e.g. influenza, HIV, malaria, infectious mononucleosis, or gastroenteritis
• Various skin inflammations, e.g. boils, pimples, acne, or abscess
• Immunological diseases, e.g. lupus erythematosus, sarcoidosis, inflammatory bowel diseases
• Tissue destruction, which can occur in hemolysis, surgery, infarction, crush syndrome, rhabdomyolysis, cerebral hemorrhage, etc.
• Reaction to incompatible blood products
• Cancers, most commonly kidney cancer and leukemia and lymphomas
• Metabolic disorders, e.g. gout or porphyria
• Thrombo-embolic processes, e.g. pulmonary embolism or deep venous thrombosis
• Persistent fever which cannot be explained after repeated routine clinical inquiries, is called fever of unknown origin.

Diseases called "fever"

As fever is a prominent symptom of many diseases, in humans and animals, it will often appear in the common appellation of diseases.

In humans

• Puerperal fever
• Scarlet fever
• Typhoid fever
• Rheumatic Fever
• Malaria, which was once called "marsh fever"

Viral hemorrhagic fevers

• Ebola fever
• Dengue fever
• Yellow fever

Drug-induced fever, which is technically a form of hyperthermia

In animals

• East Coast fever (an African disease of cattle)
• Malignant catarrhal fever (a worldwide disease of cattle)
• Rift valley fever (an African disease of sheep)
• Classical and African swine fevers (diseases of pigs)
• Milk fever, an oddly named disease of cattle; body temperature is not elevated in this disease

Management

Fever should not necessarily be treated. Most people recover without specific medical attention. People are generally advised to keep adequately hydrated. Oral rehydration solutions or water are generally used for this purpose. Excessive water may lead however to hyponatremia. Some limited evidence supports the use of tepid sponging. If the temperature reaches the level of hyperpyrexia aggressive cooling is required.

Medications

The antipyretics ibuprofen is effective in treating a fever. It is more effective than acetaminophen / paracetamol in children however both may be used together, safely. The effectiveness of acetaminophen by itself is questionable. Ibuprofen is also superior to aspirin, which is not usually recommended in children due to the risk of Reye's syndrome.