Differential diagnosis of fever of unknown origin in children.

Fever of unknown origin in children follows two main clinical patterns, namely fever of unknown origin and chronic episodic fever of unknown origin. Fever of unknown origin is characterized by daily fever persisting for more than 3 weeks. The main causes are infectious, rheumatologic disorders, and malignancy. Chronic episodic fever of unknown origin is characterized by fever lasting for a few days to a few weeks, followed by a fever-free interval and a sense of well-being. The main causes are familial Mediterranean fever, the hyper-immunoglobulin D syndrome, familial Hibernian fever, Behcet disease, the syndrome of periodic fever, aphthous stomatitis, pharyngitis and adenitis, and cyclic neutropenia.