In emergency medicine we occasionally encounter fever that won’t yield to a specific diagnosis. We speculate a viral cause and a self-limited course, but it is worth thinking through the next step. The term “fever of unknown origin” originates in internal medicine and refers to specific criteria that are appropriate for that setting. If the fever lasts three weeks, it is not necessarily consistent with a self-limited viral cause and this thought process is triggered.
Classic causes of fever of unknown origin are:
2. Connective Tissue Disease
3. Malignancy (often hematologic)
Additional noninfectious causes of elevated temperature in emergency medicine include environmental, toxicologic, and endocrine (hyperthyroidism).
Thinking about these possibilities may prompt the diagnostic process and establish the correct diagnosis early. Of course, even in the modern era, half of all cases of fever of unknown origin never have their cause discovered.(Bleeker-Rovers Medicine 2007)
Take Home Points:
-Fever of unknown origin classically is due to infection, connective tissue disease, or malignancy