Differential diagnosis of fever

1. Big picture

Fever is not a diagnosis; it is a clinical sign of inflammation, infection, malignancy, autoimmune disease, drug reaction, or impaired heat regulation. In the final exam, the examiner wants you to approach fever safely:

First: Is the patient unstable or septic? Second: Is this infectious or non-infectious? Third: Is there a localizing clue? Fourth: If no clue, is this fever of unknown origin?

The dangerous mistake is to treat every fever as “viral” or to give random antibiotics without cultures, while missing sepsis, meningitis, endocarditis, febrile neutropenia, malaria, tuberculosis, lymphoma, vasculitis, or drug fever.