Fever is a pathological process in which a thermogenic agent acts directly on the thermoregulatory center and causes a dysfunction, an increase in the thermoregulatory point or an increase in body temperature due to excessive heat production and reduced heat dissipation from various causes.
Fever can be caused by a variety of infectious and non-infectious diseases. In the identification can be approached from the following perspectives.
I. Fever type.
1. Retained fever: 39-40°C or more, with 24-hour temperature fluctuations within 1 degree, which can last for several days or weeks. Seen in the extreme stage of fever in streptococcal pneumonia, typhoid fever and typhus.
2.Flaccid fever: above 39℃, 24-hour temperature fluctuation up to 2 degrees or more, not easy to return to normal temperature. Seen in sepsis, rheumatic fever, severe tuberculosis, septic inflammatory disease, etc.
3.Intermittent fever: It is to alternate regularly with short fever period and feverless period, seen in malaria, acute pyelonephritis, etc.
4.Return fever: The body temperature can rise abruptly to more than 39℃, continue to be high for several days and then drop to normal, after several days, the fever can occur again, and so on repeatedly, see in return fever, Hodgkin’s disease, periodic fever, etc.
5.Wavy fever: The body temperature can reach 39℃ or above, last for several days and then gradually drop to normal level, after several days of fever-free period, fever again, and so on repeatedly, seen in brucellosis.
6.Irregular fever: Irregular, seen in tuberculosis, rheumatic fever, pneumonia, pleurisy, infective endocarditis, etc.
II. Etiology.
(A) Infectious diseases
In the fever causes to be investigated in the first place, including common systemic or focal infections caused by various pathogens. Infectious fever caused by bacteria is the most common.
Infectious fever mostly has the following characteristics.
1, rapid onset of fever with or without chills.
2. systemic and localized symptoms and signs.
Blood picture: white blood cell count is often higher than 1.0×10^9/L or lower than 0.5×10^9/L (the total number of white blood cells and the percentage of neutrophils can be roughly determined according to what type of pathogenic infection).
4.Tetrazolium blue test (NBT): If the neutrophil reduction NBT exceeds 20%, it suggests bacterial infection and helps to differentiate it from viral infection and non-infectious fever (normal value <10%) which can be false negative after applying hormone.
5, C-reactive protein measurement (CRP): positive suggests bacterial infection and rheumatic fever, negative is mostly viral infection.
6, neutrophil alkaline phosphatase points increase: normal value is 0 to 37, the higher the increase, the more conducive to the diagnosis of bacterial infection, when excluding pregnancy cancer, malignant lymphoma is more meaningful. It can be elevated or false positive after the application of hormones.
(B) Non-infectious diseases
1. Absorption of sterile necrotic material: physical and chemical stimulation; thrombophilia; hematologic diseases and malignancies such as leukemia, malignant histiocytosis, malignant lymphoma, colon cancer, primary hepatocellular carcinoma, etc.
2, antigen antibody reaction: allergic diseases such as drug fever, rheumatic fever; connective tissue diseases such as systemic lupus erythematosus (SIE) dermatomyositis nodular polyarteritis mixed connective tissue disease (MCTD), etc.
3, endocrine and metabolic disorders: such as hyperthyroidism, thyroid crisis, severe water loss, etc.
4, reduced skin heat dissipation: skin diseases, chronic cardiac insufficiency, etc.
5, thermoregulatory malfunction: heat stroke, sleeping pill poisoning, direct damage to the center, etc.
Non-infectious fever has the following characteristics.
1.The fever duration often exceeds 2 months, and the longer the fever duration, the greater the possibility.
2.Prolonged fever, but the general condition is fair, without obvious toxic symptoms.
3. Anemia, painless multi-site lymph node enlargement, and hepatosplenomegaly.
III. Accompanying symptoms.
1, chills mostly suggest infection, however, lymphoma, malignant histiocytoma, etc. about 2/3 also have chills. This indicates that chills are not unique to infectious diseases.
Chills are common in severe bacterial infections (lobar pneumonia, lung abscess, acute pyelonephritis, acute cholecystitis, etc.), malaria, and blood or fluid transfusion reactions. In tuberculosis, rickettsial typhoid and viral infections are rare. Generally, it is not seen in connective tissue disease.
3. Fever is often accompanied by non-specific symptoms such as dizziness, lightheadedness, headache, malaise and loss of appetite, which have no differential diagnostic significance. But the localized local symptoms have important reference value.
If fever is accompanied by neurological symptoms, such as severe headache and vomiting, impaired consciousness and convulsions, meningeal irritation signs, etc., it suggests that the lesion is in the central nervous system and encephalitis and meningitis should be considered.
In elderly patients with severe infections, there are often changes in mental status and the body temperature is not always high enough to warrant attention.
It is important to take a detailed clinical history of the febrile patient to clarify the cause, duration, fever pattern, and accompanying symptoms in order to make accurate and rapid judgments and to deal with them in a timely manner. We also hope that the patients themselves have an understanding of the fever, so that the doctor-patient communication can get twice the result with half the effort.