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    Suspicious fever of unknown origin

     

    Discussion

    Fever, defined as a core body temperature equal to or greater than 100.4°F, is one of the most common complaints that brings a child to medical attention. The most common cause of a febrile illness in a well-appearing child is usually a self-limited viral infection.1 Once a fever without a clear source lasts more than a week, it becomes FUO by definition.2

    Kawasaki disease is an acute childhood multisystemic vasculitis that can present as FUO. It is the main cause of acquired heart disease in Western countries in comparison with rheumatic heart disease in developing countries.3,4,5,6 If left untreated, KD can lead to devastating cardiac outcomes, as coronary artery aneurysms (CAAs) were reported in up to 25% of untreated patients.3,5,6 This number decreased to less than 5% after intravenous immunoglobulin (IVIG) was added to the treatment protocol.3,5 With the IVIG treatment window of 10 days or less since fever onset, one can see the importance of early recognition and treatment in avoiding cardiac complications.

    The exact etiology of KD remains largely unknown, but one hypothesis suggests an infectious trigger in genetically susceptible individuals.4,7 Infectious trigger, likely viral, was suggested because of the seasonal peaks of the illness (winter and early spring in North America) and concomitant viral infections in many KD patients. Genetics plays an important role as KD is more common in children of Asian descent, particularly Japanese children in whom the annual incidence was 265 per 100,000 children aged younger than 5 years in 2012 compared with 25 per 100,000 children aged younger than 5 years in the United States.3,4

    First described by Japanese pediatrician Dr. Tomisaku Kawasaki in 1967,6,8 KD has been traditionally classified as typical and atypical or incomplete disease. The diagnosis of typical, or complete, KD requires 5 days of persistent fever and 4 or more of the 5 diagnostic criteria shown in Table 2. It is important to note that these signs and symptoms can happen in sequence and not necessarily at the same time as presentation.4,5 Patients who have 5 days of fever and only 2 to 3 of these principal criteria can then be evaluated further according to the American Heart Association (AHA) algorithm (shown in Figure) for incomplete disease. The term “incomplete” is preferable to “atypical” as incomplete KD has similar clinical course to complete disease and nothing atypical is present other than fewer principal clinical features at presentation.7 Infectious causes, specifically viral, are among the main differential diagnoses of KD (Table 3).

    KD in infants aged younger than 6 months

    Kawasaki disease is a childhood vasculitis with 50% of cases occurring between ages 6 months and 2 years.5,9 The disease in infants aged younger than 6 months includes approximately 10% of all cases,5 and this age group is at higher risk for delayed diagnosis and coronary artery abnormalities.3,5,6,9 The nonspecific clinical features and absence of specific tests make it difficult to diagnose KD in general, and it is even more challenging in these infants because infantile KD can present with prolonged fever and irritability with no other clinical signs and symptoms (ie, no cervical lymphadenopathy, no conjunctivitis, and no hands or feet edema).3,6,7 Subsequently, maintaining a high index of suspicion in infants aged younger than 6 months with persistent unexplained fever is the key for diagnosis and timely treatment.

    Related: Coronary artery lesions in Kawasaki disease are related to gene polymorphisms

    The recent AHA guidelines recommend that infants aged younger than 6 months with 7 or more days of fever even without any other clinical manifestations should undergo laboratory investigation for incomplete KD.3

    As was seen in this patient, KD in infants aged younger than 6 months can be misdiagnosed as febrile UTI or aseptic meningitis due to pyuria and pleocytosis, respectively, which might lead to delayed diagnosis and late treatment.

    NEXT: Treatment of KD

    Lauren Coogle, MD
    Dr Coogle is a pediatric resident, Wright State University, Dayton Children’s Hospital, Dayton, Ohio.
    Shafee Salloum, MD, FAAP
    Dr Salloum is assistant professor of Pediatrics, Boonshoft School of Medicine, Wright State University, and Dayton Children’s Hospital, ...

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