Fever of unknown origin

Fever of unknown origin is, by definition, a fever persisting for more than 3 weeks with no obvious clinical cause after adequate evaluation. It can be caused by infections, malignant conditions, and rheumatic or connective-tissue diseases such as temporal arteritis and polymyalgia rheumatica. Renal cancer, leukemia, and lymphomas are the most likely malignancies to cause fever. Other conditions associated with fever of unknown origin include pheochromocytoma, drug fever, and thyrotoxicosis. Empirical antimicrobial therapy is generally discouraged, unless clinically warranted, during the diagnostic evaluation of a patient with fever of unknown origin, since antibiotics may reduce the yield of diagnostic testing and rarely result in a lasting resolution of symptoms.