Approach
Roseola is usually diagnosed based on the classic presentation of a previously healthy infant, 6 to 24 months of age, with a sudden onset of high fever for 3 to 7 days. Resolution of fever is associated with the onset of discrete red macules and papules on the trunk and extremities. For patients with this classic presentation, a clinical diagnosis can be made based on physical examination findings and history (usually at the time of resolution of fever). Diarrhoea and upper respiratory symptoms are also reported, though not diagnostic. Laboratory investigation is seldom necessary. An FBC with differential may initially show an elevated WBC, which may evolve into a low WBC with relative neutropenia and atypical lymphocytosis.[10] There may be sterile pyuria in some infants with roseola.[13]
Physical examination
Physical examination findings are limited early in the disease course, though up to 15% of children will present with an episode of febrile seizure. An enanthem (intra-oral eruption) composed of red papules on the soft palate and uvula (Nakayama's spots) has been described.[10][14] The typical exanthem, which occurs 3 to 5 days after the onset of the illness, consists of pink-red macules and papules on the trunk, neck, and proximal extremities, and occasionally on the face. The exanthem fades within a few hours to days. Other signs associated with roseola include tympanic inflammation, peri-orbital oedema, bulging anterior fontanelle, lymphadenopathy (cervical, post-auricular, and/or occipital), and abdominal pain.[15]
Laboratory investigations
Serology is rarely performed and may be needed only in children with complicating medical factors (e.g., encephalitis). Measuring IgM levels is not reliable in the diagnosis of human herpesvirus (HHV)-6 or HHV-7 infection. IgG is of diagnostic value for HHV-6/HHV-7 primary infections when it goes from undetectable to positive.[9] Polymerase chain reaction detection of viral DNA may be of use, especially in those who are immunosuppressed (e.g., post bone marrow transplant), and is an adjunct to serology. However, distinguishing between active and latent infection can be problematic; nevertheless, special polymerase chain reaction assays are available to distinguish between latent (chromosomally integrated [ciHHV-6]) versus active infection. Other diagnostic tools include viral culture and electron microscopy, though these are used infrequently in the acute clinical setting. Viral culture is not often used because, in isolation, it cannot accurately distinguish acute primary HHV-6/HHV-7 infection from latent or persistent infection. Also, it is not commercially available.[16]
Skin biopsy
This is rarely performed. Biopsy of the affected skin shows findings of non-specific viral exanthem with a sparse, lymphocytic perivascular and dermal infiltrate.
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