Fever of unknown origin refers to fevers higher than 101 degrees Fahrenheit rectally without an immediately identifiable cause or other symptoms that last at least two weeks. A fever in a toddler who can't describe any other symptoms she's having to you can be more difficult to evaluate, especially if physical evaluation by your physician turns up no clues as to the source. Fevers account for 33 percent of all doctor's visits in young children, professor of infectious diseases at Baylor University Dr. Debra Palazzi reports on the UpToDate website.
Frequency
The cause of fever can be difficult to determine, with 20 percent of children with fever have no obvious source of infection, pediatrician Dr. Larry Baraff of the University of California states in the December 2000 "Annals of Emergency Medicine." In between 25 and 67 percent of children with fever, no cause is found, Dr. Elise W. van der Jag reports in the "AAP Textbook of Pediatric Care."
Causes
Most fevers of unknown origin have one of three causes: infectious diseases, connective tissue disorders and cancers, according to Palazzi. Infectious diseases, with bacterial infection more common than viral infection, make up between 40 and 60 percent of fevers of unknown origin and comprise the largest cause of this condition in children. Autoimmune or connective tissue diseases, such as juvenile arthritis or systemic lupus erythematosus, account for 7 to 20 percent but generally affect children older than 6. Cancer causes between 1.5 and 6 percent of fevers of unknown origin, with leukemia the most common cancer that causes this symptom in children, according to van der Jagt.
Atypical Presentation
Fevers of unknown origin caused by infection can be difficult to diagnose because they have an atypical presentation, without the signs and symptoms normally seen in an infection. In boys younger than 1 with fevers without a source, 3 to 4 percent have occult urinary tract infections, which occur mostly in uncircumcised boys. Between 8 and 9 percent of girls younger than 2 have occult urinary tract infections. Girls develop these infections more frequently than boys, Baraff reports.
Unusual Causes
One cause of fevers of unknown origin before age 3 is periodic fever, aphthous stomatitis, pharyngitis, and cervical adenopathy. This recurrent autoinflammatory syndrome lasts three to five days and recurs every three to six weeks. Other types of recurrent fever associated with gene mutations include familial Mediterranean fever and cyclic neutropenia, a low white blood cell count.
References
- Pediatric Care Online: AAP Textbook of Pediatric Care: Chapter 182: Fever of Unknown Origin; Elise W. van der Jagt, M.D.; August 2008
- UpToDate; Etiologies of Fever of Unknown Origin in Children; Debra Palazzi, M.D., et al.; April 2011
- "Annals of Emergency Medicine"; Management of Fever Without Source in Infants and Children; L. Banaff, M.D.; December 2000
- "World Journal of Pediatrics"; Fever of Unknown Origin in Children: A Systematic Review; Amy Chow, et al; February 2011
