infectious diseases
Fever of Unknown Origin (FUO)
Etiology of FUO
Causes of FUO are usually divided into 4 categories ( see Table: Some Causes of Fever of Unknown Origin (FUO) ): Infections (25 to 50%) Connective tissue disorders (10 to 20%) Neoplasms (5 to 35%) Miscellaneous (15 to 25%) Infectionsare the most common cause of FUO. In patients with HIV infection, opportunistic infections (eg, tuberculosis; infection by atypical mycobacteria, disseminated fungi, or cytomegalovirus) should be sought. Common connective tissue disordersinclude systemic lupus erythematosus, rheumatoid arthritis, giant cell arteritis, polymyalgia rheumatica, thyroiditis, vasculitis, and juvenile rheumatoid arthritis of adults (adult Still disease). Themost common neoplastic causesare lymphoma, leukemia, renal cell carcinoma, ovarian carcinoma, atrial myxoma, Castleman disease, hepatocellular carcinoma, and metastatic carcinomas. However, the incidence of neoplastic causes of FUO has been decreasing, probably because they are being detected by ultrasonography and CT, which are now widely used during initial evaluation of fever. Important miscellaneous causesinclude drug reactions, deep venous thrombosis, recurrent pulmonary emboli, sarcoidosis, inflammatory bowel disease, and factitious fever. No cause of FUO is identified in about 10% of adults. 