Fever of unknown origin

• Causes
• Subtypes

A fever of unknown origin (FUO) is used to describe a temperature that has been raised for at least three weeks without a possible cause having been found despite lots of tests being done at a hospital. Unlike a common fever, the causes of FUO are harder to find. A list of some of the causes of an FUO is given below.

Causes of a fever of unknown origin

1. Infections
   • Tuberculosis (especially outside the lungs)
   • Infective endocarditis
   • Osteomyelitis
   • Abscesses (collections of pus around an infection):
     • Abdominal
     • Pelvic
     • Dental
   • Sinusitis
   • Cytomegalovirus
   • Epstein-Barr virus
   • Human immunodeficiency virus
   • Lyme disease
   • Prostatitis (infection of the prostate)
2. Malignancies
   • Chronic leukaemia
   • Lymphoma
   • Metastatic cancers
   • Renal cell carcinoma of the kidney
   • Colon cancers
   • Hepatocellular carcinoma
   • Adenocarcinoma of the pancreas
3. Autoimmune conditions
   • Polymyalgia rheumatica (PMR)
   • Temporal (giant cell) arteritis
   • Rheumatoid arthritis
   • Rheumatoid fever
   • Inflammatory bowel disease
   • Reactive arthritis
   • Systemic lupus erythematosus (SLE)
   • Vasculitis
4. Miscellaneous
   • Some drugs
   • Complications from cirrhosis of the liver
   • Hepatitis
   • Deep vein thrombosis
   • Sarcoidosis

Patient subtypes

There are some types of patients are particularly prone to some specific infections. These include:

1. Hospitalised patients: Infection of the veins, pulmonary embolism (PE), bowel infections, and drug-induced fever.
2. Immune-compromised patients: In most of these cases, the fever is caused by opportunistic bacterial infections. These patients are usually treated with broad-spectrum antibiotics to cover the most likely bugs.
3. HIV associated: HIV itself can cause a fever that is often hard to identify and could be an FUO. However, HIV also leaves a patient open to certain types of infections including: Mycobacterium avium-intracellulare complex, Pneumocystis carinii pneumonia, and cytomegalovirus.

References

1. Bor DH. Approach to the adult with a fever of unknown origin [online], UpToDate, 2006. Available at URL: http://www.uptodate.com (last accessed 24/08/06)
2. Bor DH. Etiologies of fever of unknown origin in adults [online], UpToDate, 2006. Available at URL: http://www.uptodate.com (last accessed 24/08/06)
3. Kumar P, Clark M. Clinical Medicine (Fifth Edition). London, Saunders, 2005.
4. Murtagh, J. General Practice (Third Edition). North Ryde, McGraw-Hill Australia, 2003.