Cytophagic histiocytic panniculitis after H1N1 vaccination: a case report and review of the cutaneous side effects of influenza vaccines.

Cytophagic histiocytic panniculitis (CHP) is a rare disease mostly caused by viral infections and/or lymphoproliferative diseases. We describe a case of CHP associated with H1N1 vaccine during the winter 2009-2010 vaccination campaign and discuss the cutaneous side effects of influenza vaccines. A 6-year-old child presented with inflammatory subcutaneous nodules, which had appeared 1 month after the first injection of H1N1 vaccine and 1 week after the second injection. There was no history of recent infection. The skin lesions spontaneously disappeared without scarring. In CHP the abnormal cytokine secretion from neoplastic or reactive T cells promotes monocyte-macrophage activation and haemophagocytosis. Vaccination is not a common cause of CHP, but it seems possible that, as in infectious diseases, reactive T cells to the vaccine antigen could trigger CHP.