Fever of unknown origin in older adults.

Evaluation of elderly patients who have fever of unknown origin (FUO) requires a different perspective from that needed for young patients. Differential diagnosis often varies with age, and presentation of the disease frequently is nonspecific and symptoms difficult to interpret. Noninfectious diseases are the most frequent cause of FUO in the elderly and temporal arteritis the most frequent specific cause. Tuberculosis is the most common infectious disease associated with FUO in elderly patients. FUO often is associated with treatable conditions in the elderly. Therefore, intensive, accelerated evaluation is necessary, as the lack of physiologic reserve makes this population vulnerable to irreversible changes and functional deterioration.