FEVER OF UNKNOWN ORIGIN: SOME SELECTED CAUSESTuberculosisFor tuberculosis to cause an FUO (Fever of Unknown Origin), it must typically manifest as either disseminated or primarily extrapulmonary disease. Approximately 25% of the time, a tuberculin skin test will be negative in this situation. The diagnosis of extrapulmonary tuberculosis, in particular, can be challenging. A diagnosis may be achieved with a thoracoscopic lung biopsy or liver biopsy (manifesting as granulomatous hepatitis). Urinalysis may provide initial diagnostic clues to kidney involvement, and back pain may hint at spinal involvement. A bone marrow biopsy can be diagnostic.
Infective EndocarditisClinical history, physical examination, and blood cultures are chief aids in the diagnosis of endocarditis. Any evidence of microscopic hematuria, circulating immune complexes, and systemic signs of inflammation such as anemia or leukocytosis are also consistent. When endocarditis is suspected, and blood cultures are non-diagnostic, additional tests should be performed. Lysis-centrifugation system blood cultures and specific serologic analysis should be considered. Culture-negative pathogens are more easily diagnosed, owing to improved culturing techniques. However, Bartonella, Brucella, Coxiella, and the fastidious gram-negative HACEK organisms (Haemophilus parainfluenzae, H. influenzae, H. aphrophilus, H. paraphrophilus, Actinobacillus actino-mycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella species) account for the majority of cases of culture-negative endocarditis and should be considered when clinically indicated.
CytomegalovirusCytomegalovirus is a common cause of a prolonged febrile illness. Cytomegalovirus often appears without the diagnostic clues of sore throat, lymphadenopathy, and splenomegaly that may be present in infection with Epstein-Barr virus. In most cases, atypical lymphocytosis is present on peripheral smear. Subtle abnormalities in liver-associated enzymes are potential diagnostic clues. Immunoglobulin M and G antibodies should be present and their levels elevated, and the serum cytomegalovirus antigen level should be high.*155/348/5* rxnorth.com