What is a Fever of unknown origin?

A fever of unknown origin (FUO) is a fever that remains undiagnosed after one week of investigation in a hospital. It is a diagnosis of exclusion, made when common causes of fever have been ruled out.

Causes of FUO can be broadly categorised into:

- Infectious diseases, such as malaria, typhoid fever, brucellosis, and human immunodeficiency virus (HIV).

- Malignant diseases, such as leukemia, lymphoma, and disseminated carcinoma.

- Rheumatologic diseases, such as systemic lupus erythematosus, vasculitis, and Still's disease.

- Miscellaneous causes, such as drug reactions, factitious disorders, and foreign body reactions.

The diagnostic approach to FUO typically involves clinical history, physical examination, laboratory tests, and imaging studies. Blood tests may include complete blood count, urinalysis, liver function tests, renal function tests, and serologies for common infectious diseases. Imaging studies may include chest radiography, abdominal ultrasonography, and computed tomography (CT) scan. In some cases, additional tests such as lumbar puncture, bone marrow aspiration, and biopsy may be needed to establish the diagnosis.

The management of FUO depends on the underlying cause. For infectious causes, specific antimicrobial therapy will be prescribed. In cases of malignancy, appropriate chemotherapy or radiation therapy will be initiated. For rheumatologic diseases, immunomodulatory medications will be used. Supportive care, such as intravenous fluids, antipyretics, and analgesics, is provided as needed.