A technical term, not just a fever without obvious source! Essentially presence of confirmed fever for 8 days or more in a child in whom a careful thorough history and physical examination, and preliminary laboratory data fail to reveal a probable cause.
Long list of possible causes, long lists of possible tests – do thorough history and repeated examinations, then follow the clues!
In kids, infection is the commonest cause. But can be connective tissue disorder, or malignancy.
Beware factitious fever – admission sensible.
If possible, stop all drugs. Antipyretics may obscure the pattern of fever, and can occasionally be its cause (drug fever is one cause).
Unless the child is critically ill, try not to give antibiotics. If the diagnosis remains obscure, go back and take the history again, examine the child (fully) again, send the specimens again!
Special points in history/examination
- Travel – malaria can present 6-12 months later. Typhoid.
- Ethnicity – tuberculosis
- Outdoor activities – rats/ticks as vectors of infectious diseases
- Animal contact – cows/sheep (brucellosis), cats (cat scratch)
- Mouth ulcers (IBD, Behcets, PFAPA)
- Periodicity – see Periodic fever
- Sinus tenderness, nasal congestion (sinusitis)
- Bone/spine tenderness – discitis, vertebral osteomyelitis
- 3 sets of blood cultures, different sites, different times (at least a few hours apart), off antibiotics – standard for endocarditis
- EBV, CMV
- LDH, CK
- Urine/stool culture
- Swab everything!