The traditional definition of fever of unknown origin (FUO) is a temperature rising above 38.3°C (101°F) on several occasions over a period of more than 3 weeks, for which no diagnosis has been reached despite 1 week of inpatient investigation.Here is an elegant perspective published in the NEJM on the new FUO, one which now includes various groups: classic, nosocomial, neutropenic,and HIV-associated.
Of note, even with advanced diagnostics, no diagnosis is made in 50+ percent of modern era FUOs. As suggested by the writer, many of these patients are critically ill with multiple conditions and devices. The (potential) causes of fever are numerous making the diagnosis increasingly more challenging.
The result, fever of too many origins (FTMO).
Vexing.
