fever of unknown origin as an onset for late-onset systemic lupus erythematous

introduction systemic lupus erythematous (sle) is among rheumatic diseases of unknown etiology. fever of unknown origin (fuo) has been rarely reported to be the presenting sign of sle. presence of four or more sle criteria is diagnostic for the disease. however, presentations may occur serially which make it much more difficult to diagnose an already questioned fuo. case presentation our case of sle, presenting with a long history of unidentified fuo, was a 73-year-old man treated due to various diagnoses in different medical services before referring to the department of infectious diseases at imam khomeini hospital. none of the previous treatments were effective to resolve his fever. in infectious ward, we performed multiple diagnostic tests to approach the fuo, and the patient serially presented some criteria of sle. therefore, we referred the patient to the rheumatology ward with late-onset systemic lupus erythematous (lo-sle) for more work ups and management. discussion fuo in elderly has a wide range of differential diagnoses and infection with tuberculosis, immunologic and pulmonary diseases, other multisystem diseases, tumors, and medications are presented on the top. sle has rarely been mentioned after the age of 50 as a cause of fuo; but due to more severe damages to the body organs, its potential should be considered. although our case presented only three criteria of sle, this diagnosis was confirmed and treated by the rheumatologist; thus the symptoms and signs gradually improved.