Acute hemorrhagic edema of childhood after H1N1 immunization.

Acute hemorrhagic edema (AHE) is an uncommon self-limited disorder affecting young children triggered by infection, drugs, or immunization. A 2-year-old boy was observed due to sudden onset of painful and edematous purpuric papular and plaque lesions of the face and upper extremities that started 2 weeks after H1N1 immunization. The patient also developed exuberant edema on the face and dorsum of the hands. Complete blood count, biochemistry, and urinalysis results were normal. Histopathological examination revealed perivascular and periadnexial lymphocytic infiltrate with neutrophils and eosinophils, and leukocytoclastic vasculitis. Blood PCR technique was negative to several viruses, namely adenovirus, cytomegalovirus, Epstein Barr, enterovirus, HHV6, parvovirus B19, and H1N1. Symptomatic treatment and parents reassurance was promptly provided. However, new lesions continued to develop and in this setting systemic corticosteroid was prescribed. Complete clinical resolution was achieved within 2 weeks and no relapse was observed. The temporal relationship with H1N1 immunization, absence of previous drug intake, as well as exclusion of viral infections led the authors to propose that H1N1 vaccine was the predisposing factor in AHE development in our patient. To our best knowledge, this is the first reported association between AHE and H1N1 immunization.