In 1972, McClung identified fever of unspecified origin in children as any disease with a fever that was not diagnosed for more than 3 weeks of outpatient or more than 1 week of inpatient examination. He also argued that in most cases the temperature should exceed 39 ° C for rectal measurement.
McClung made it clear that this definition is arbitrary and serves the purpose of his work. In 1975, Pizzo described 100 children with a fever of unknown origin, which he simply identified as an unexplained temperature above 38.5 ° C, noted more than 4 times over at least 2 weeks.
In 1977, Lohr reported on 54 children with fever of unknown origin, using the criteria for the duration of the fever proposed by McClung (3 weeks on an outpatient basis or 1 week on inpatient conditions), but he considered the temperature above 38.3 ° C rather than 39 ° C like McClung.
The term fever of unknown origin is mainly used in cases where there are no specific changes, even of an obscure nature. For example, a child with prolonged fever and pneumonia would be more accurate to say as a patient with “pneumonia of unknown origin”, rather than with fever of unknown origin.
If there are specific symptoms, even when their nature has not been established (rash, hepatosplenomegaly, lymphadenopathy), the term fever of unknown origin is controversial to some extent and should be used with caution. If a patient has only nonspecific symptoms (malaise, loss of body weight, fatigue, loss of appetite), then without any doubt you can use the term fever of unknown origin.
It is clear that for research and clinical purposes it is necessary to “mark the exact and specific definition of fever of unknown origin. However, the clinician, taking a child with an unexplained fever for a long time, must take into account many factors besides the duration and magnitude of the temperature. How sick is the baby?
Is there a significant loss of body weight? Can a patient come for repeated examinations and treatment? When taking into account these factors, the doctor may be faced with the need for urgent examination of the patient to identify the causes of fever of unknown origin (LDL).
When an early diagnosis of fever of unknown origin and a more rapid diagnostic examination than expected according to the criteria of Petersdorf, McClung and Pizzo, the probability of detecting certain diseases will differ from the results reported by these authors. The longer the fever, the less likely it is caused by acute or self-sustaining diseases. In addition, as the duration of fever increases, the chances of detecting infectious diseases decrease.