Introduction
Fever of unknown origin (FUO) is a challenging diagnostic dilemma. Defined as a fever of 100.9oF (38.3oC) or higher lasting at least three weeks with an unrevealing diagnostic work up1, FUO’s in adults typically represent unusual presentations of common illnesses. Most often, the condition resolves without a specific diagnosis being made2.
The differential diagnosis for FUO is extensive. A helpful approach is to consider infectious, inflammatory, and malignant diseases, as well as miscellaneous conditions such as thyroiditis, thromboembolic disease, and factitious fever. A comprehensive history emphasizing social and travel components should precede a complete physical examination, with laboratory tests and imaging guided by pertinent findings on history and exam.