A four-year-old boy with fever, rash, and arthritis.

The triad of fever, rash, and arthritis in a hospitalized child suggests an inflammatory, infectious, or postinfectious process in most cases; however, malignancy must be considered. The most common causes in this age group are inflammatory conditions, including Kawasaki disease, Henoch-Schönlein Purpura, serum sickness-like reaction, and juvenile idiopathic arthritis. Other rarer inflammatory processes can present with this triad of symptoms such as Cryopyrin-related diseases (autoinflammatory disorders), urticarial vasculitis, and systemic lupus erythematosus. We will discuss the differential diagnosis and inpatient management of fever, rash, and arthritis in a young child, focusing on inflammatory conditions. The important features which can help distinguish these conditions include the nature of the rash, associated signs or symptoms, time course of the eruption, and characteristic laboratory and/or histologic findings.