IgM against rubella in a case of maculopapular exanthema caused by Epstein-Barr virus

Because the variety of virus causing maculopapular exanthemas the definitive diagnosis of these process can be complicated. Te aim of this study is to present a case that raised problems in the differential diagnosis between the Epstein-Barr and the rubella viruses. A girl twenty one months-old, immunised at the 15 months of age with MMR vaccine, which presented a maculopapular exanthema of 5 days of evolution in face, neck and extremities accompanied by febricula, cough, coriza and cervical adenopathies was studied. The hemogram and the biochemical tests revealed a discreet leucocytosis (with prevalence of lymphomonocytes) and elevation of transaminases. The serological results showed a profile of recent infection by Epstein Barr virus (positive result for IgM-VCA and negative for IgGVCA and IgG-EBNA). Other serological positive results included IgM and IgG against rubella (the IgG-rubella avidity index was <80%). The PCR performed in pharyngeal exudates was only positive for Epstein Barr virus. Epstein Barr virus, besides being a possible agent producing of exanthemas, is a polyclonal stimulator of B lymphocytes. In the present case its etiologic role seems to be evident. The detection of Epstein-Barr by means of PCR, the serological profile of recent infection by this virus, the antecedents of immunization with MMR vaccine and the result of high avidity IgG-rubella suggest that the IgM positive result against the late agent was caused by a polyclonal stimulation of lymphocytes generated after the MMR vaccination.