Белгісіз себепті қызба (Негізгі себебі анықталмаған қызба)

Fever of unknown origin (FUO) refers to a condition in which the patient has an elevated temperature (fever) but, despite investigations by one or more qualified physicians, no explanation is found. If the cause is found it is usually a diagnosis of exclusion, eliminating all possibilities until only the correct explanation remains.

This refers to the original classification by Petersdorf and Beeson. Studies show there are five categories of conditions:
infections (e. g. abscesses, endocarditis, tuberculosis, and complicated urinary tract infections),
neoplasms (e. g. lymphomas, leukaemias),
connective tissue diseases (e. g. temporal arteritis and polymyalgia rheumatica, Still's disease, systemic lupus erythematosus, and rheumatoid arthritis),
miscellaneous disorders (e. g. alcoholic hepatitis, granulomatous conditions), and
undiagnosed conditions.

Nosocomial FUO refers to pyrexia in patients that have been admitted to hospital for at least 24 hours. This is commonly related to hospital associated factors such as surgery, use of a urinary catheter, intravascular devices (i. e. "drip", pulmonary artery catheter), drugs (antibiotic induced Clostridium difficile colitis, drug fever), and/or immobilization (decubitus ulcers). Sinusitis in the intensive care unit is associated with nasogastric and orotracheal tubes. Other conditions that should be considered are deep vein thrombophlebitis, pulmonary embolism, transfusion reactions, acalculous cholecystitis, thyroiditis, alcohol/drug withdrawal, adrenal insufficiency, and pancreatitis.

Immunodeficiency can be seen in patients receiving chemotherapy or in hematologic malignancies. Fever is concomitant with neutropenia (neutrophil <500/uL) or impaired cell mediated immunity. The lack of immune response masks a potentially dangerous course. Infection is the most common cause.

HIV infected patients are a subgroup of the immunodeficient FUO, and frequently have fever. The primary phase shows fever since it has a mononucleosis like illness. In advanced stages of infection fever mostly is the result of a superimposed infections.

Unless the patient is acutely ill, no therapy should be started before the cause has been found. This is because non specific therapy is rarely effective and may delay the diagnosis. An exception is made for neutropenic (low white blood cell count) patients or patients who are severely immunocompromised in which delay could lead to serious complications. After blood cultures are taken this condition is aggressively treated with broad spectrum antibiotics. Antibiotics are adjusted according to the results of the cultures taken. HIV infected people with pyrexia and hypoxia will be started on medication for possible Pneumocystis jirovecii infection. Therapy is adjusted after a diagnosis is made.

Since there is a wide range of conditions associated with FUO, prognosis depends on the particular cause. If after six to twelve months no diagnosis is found, the chances of ever finding a specific cause diminish. Under those circumstances, the prognosis is good.