Thymic involution mimicking thymic dysplasia: a consequence of transfusion-induced graft versus host disease in a premature infant.

A premature infant with ostensibly normal immunologic function received two exchange blood transfusions for hyperbilirubinemia and several blood and platelet transfusions for pancytopenia. A fatal graft vs host reaction (GvHR) ensued that was diagnosed by skin biopsy one day prior to death at age 40 days. Autopsy revealed characteristic alterations of GvHR in the spleen, lymph nodes, gut, and liver. In addition the thymus was small (3.5 g), lymphoid-depleted, lacked corticomedullary demarcation and Hassall's corpuscles, and demonstrated lymphocyte invasion and injury of epithelial cells. The thymic cytomorphology acquired added meaning when it was discovered that a chest roentgenogram obtained at one day of age demonstrated a normal thymic shadow. It is concluded that the GvHR induced a direct injury to the thymic epithelium, resulting in an acquired form of thymic dysplasia. The theoretical implications of this observation are considered.