ABSTRACT
This chapter discusses the classical form of pyrexia of unknown origin, most simply defined as pyrexia that lasts for longer than three weeks and remains undiagnosed following initial clinical assessment and investigations, comprising three days of inpatient investigation or two physician visits. In general, efforts should be made to reach a diagnosis before initiating empirical treatment that may mask or even worsen the underlying condition. However, therapeutic trials of corticosteroids, antibiotics or anti-tuberculous chemotherapy may be justified in patients who are extremely unwell. Investigation should be tailored to the findings elicited by careful clinical assessment, as a blanket approach is both wasteful of resources and likely to lead to misleading false-positive results. Colonoscopy or flexible sigmoidoscopy may reveal inflammatory bowel disease, neutropenic or pseudomembranous colitis, diverticulitis or malignancy, whereas OGD may be diagnostic of upper gastrointestinal malignancy.
