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The definition of FUO requires an immunologically normal host
with oral or rectal temperature ⩾38.0°C (100.4°F) at least twice
a week for more than 3 weeks, a noncontributory history and physical
examination, and 1 week of outpatient investigation.6-9 Early
diagnostic studies normally include a complete blood cell count;
lactate dehydrogenase (LDH); uric acid; urinalysis and culture;
chest roentgenogram; tuberculin skin test; erythrocyte sedimentation
rate (ESR) or C-reactive protein (CRP); and, in the older child,
a titer of antinuclear antibodies. Management of patients with comorbidity factors
such as acquired or congenital immunodeficiency, neutropenia, and
occurrence of fever during prolonged hospital stays is not considered
in the following discussion.
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The greatest clinical concern in evaluating FUO is identifying
patients whose fever has a serious or life-threatening etiology
for whom a delay in diagnosis could jeopardize successful intervention.
Cancer and severe bacterial infections are the causes most frequently
discussed and most likely to influence diagnostic and management
approaches. However, the vast majority of children with prolonged
FUO resolve their illnesses without a diagnosis and do not exhibit
long-lasting effects. Therefore, it appears appropriate for most
children to delay extensive diagnostic evaluation until the child
has remained febrile for at least 6 weeks.
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Because of the ready availability of more sensitive serologic
assays and more precise radiographic scanning procedures, the etiologies of FUO
in children, as well as in adults, have changed over the past three
decades (Table 228-1). The most striking
change has been the virtual elimination of laparotomy as a final
step in evaluation, a procedure routinely recommended in the 1970s,
but now eliminated due to advances in radiologic imaging technology.
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Three newly defined infectious diseases now account for a moderate
number of cases: Epstein-Barr virus infection, cat-scratch disease,
and Lyme disease. All three can be confirmed with serologic assays
showing both IgM and, later, IgG antibodies to the respective pathogens.
Cat-scratch disease can also be confirmed with compatible liver
lesions documented by abdominal sonograms or CT scans.
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Two-thirds of children who now present with fever of unknown
origin resolve their fever without determination of a cause, in
contrast to only 10% to 20% in a series published 20
to 30 years ago.7-12 In addition, a higher percentage
of children with malignancies is ...