Fever of Unknown Origin

Fever in pediatric patients represents one of the most common indications for seeking medical attention. While most infants and children with fever will have self-limited viral infections, some children will exhibit prolonged fever without an obvious source, concerning for a more serious illness. The differential diagnosis of prolonged fever of unknown origin (FUO) in children most commonly includes infectious etiologies, but non-infectious conditions, such as malignancy and rheumatologic conditions, also require consideration. A logical and stepwise approach to clinical investigation of FUO is important given the broad differential diagnosis. This chapter will discuss the etiology and work-up of pediatric FUO and discuss the common etiologies and plan for management in the inpatient and outpatient setting.