Fever (also known as pyrexia or controlled hyperthermia) is a common medical signcharacterized 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, in general, 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 that 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 very high temperatures, treatment to reduce fever is often not necessary; however, antipyretic medications can be effective at lowering the temperature, which may improve the affected person's comfort.
Fever differs from uncontrolled 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.
As a person's temperature increases, there is, in general, 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 that 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 very high temperatures, treatment to reduce fever is often not necessary; however, antipyretic medications can be effective at lowering the temperature, which may improve the affected person's comfort.
Fever differs from uncontrolled 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.
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; 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.
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; 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 an intracranial hemorrhage. Other possible causes include sepsis, Kawasaki syndrome, neuroleptic malignant syndrome, drug effects, serotonin syndrome, and thyroid storm. Infections are the most common cause of fevers, however as the temperature rises other causes become more common. Infections commonly associated with hyperpyrexia include: roseola, rubeola and enteroviralinfections. Immediate aggressive cooling to less than 38.9 °C (102.0 °F) has been found to improve survival. Hyperpyrexia differs fromhyperthermia 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.
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 an intracranial hemorrhage. Other possible causes include sepsis, Kawasaki syndrome, neuroleptic malignant syndrome, drug effects, serotonin syndrome, and thyroid storm. Infections are the most common cause of fevers, however as the temperature rises other causes become more common. Infections commonly associated with hyperpyrexia include: roseola, rubeola and enteroviralinfections. Immediate aggressive cooling to less than 38.9 °C (102.0 °F) has been found to improve survival. Hyperpyrexia differs fromhyperthermia 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.
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, or abscess
- Immunological diseases, e.g., lupus erythematosus, sarcoidosis, inflammatory bowel diseases, Kawasaki disease
- 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
Pathophysiology
Temperature is ultimately regulated in the hypothalamus. A trigger of the fever, called a pyrogen, causes a release of prostaglandin E2 (PGE2). PGE2 then in turn acts on the hypothalamus, which generates a systemic response back to the rest of the body, causing heat-creating effects to match a new temperature level.
In many respects, the hypothalamus works like a thermostat.When the set point is raised, the body increases its temperature through both active generation of heat and retaining heat. Vasoconstriction both reduces heat loss through the skin and causes the person to feel cold. If these measures are insufficient to make the blood temperature in the brain match the new setting in the hypothalamus, then shivering begins in order to use muscle movements to produce more heat. When the fever stops, and the hypothalamic setting is set lower; the reverse of these processes (vasodilation, end of shivering and nonshivering heat production) and sweating are used to cool the body to the new, lower setting.
This contrasts with hyperthermia, in which the normal setting remains, and the body overheats through undesirable retention of excess heat or over-production of heat. Hyperthermia is usually the result of an excessively hot environment (heat stroke) or an adverse reaction to drugs. Fever can be differentiated from hyperthermia by the circumstances surrounding it and its response toanti-pyretic medications.
Temperature is ultimately regulated in the hypothalamus. A trigger of the fever, called a pyrogen, causes a release of prostaglandin E2 (PGE2). PGE2 then in turn acts on the hypothalamus, which generates a systemic response back to the rest of the body, causing heat-creating effects to match a new temperature level.
In many respects, the hypothalamus works like a thermostat.When the set point is raised, the body increases its temperature through both active generation of heat and retaining heat. Vasoconstriction both reduces heat loss through the skin and causes the person to feel cold. If these measures are insufficient to make the blood temperature in the brain match the new setting in the hypothalamus, then shivering begins in order to use muscle movements to produce more heat. When the fever stops, and the hypothalamic setting is set lower; the reverse of these processes (vasodilation, end of shivering and nonshivering heat production) and sweating are used to cool the body to the new, lower setting.
This contrasts with hyperthermia, in which the normal setting remains, and the body overheats through undesirable retention of excess heat or over-production of heat. Hyperthermia is usually the result of an excessively hot environment (heat stroke) or an adverse reaction to drugs. Fever can be differentiated from hyperthermia by the circumstances surrounding it and its response toanti-pyretic medications.
Management
Fever should not necessarily be treated. Most people recover without specific medical attention.In general, people are advised to keep adequately hydrated. Oral rehydration solutions or water are generally used for this purpose. Excessive water may lead however tohyponatremia. Some limited evidence supports the use of tepid sponging. If the temperature reaches the level of hyperpyrexia aggressive cooling is required.
Medications
The antipyretic 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.
Fever should not necessarily be treated. Most people recover without specific medical attention.In general, people are advised to keep adequately hydrated. Oral rehydration solutions or water are generally used for this purpose. Excessive water may lead however tohyponatremia. Some limited evidence supports the use of tepid sponging. If the temperature reaches the level of hyperpyrexia aggressive cooling is required.
Medications
The antipyretic 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.
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