Thrombocytopenic purpura during the incubation period of rubella.

A child with idiopathic thrombocytopenic purpura (ITP) which started eight days before the appearance of rubella rash is described. All previous reports described ITP after or occasionally simultaneous with the onset of rubella rash. The onset of purpura in this patient was during the incubation of rubella before the initiation of immune response, suggesting that in some patients the mechanism of platelet damage in ITP associated with rubella is through a direct effect of the virus, rather than by circulating antibodies.