[Blueberry muffin baby: the pathogenesis of cutaneous extramedullary hematopoiesis].

Two neonates exhibited the clinical picture of the "blueberry muffin baby" at delivery. The integument manifested petechiae and purpuric magenta-colored macules, papules, and plaques, as well as blueberry-colored ecchymoses. These findings led to the diagnosis of a connatal cytomegalovirus infection and fetal erythroblastosis, respectively. The hemorrhagic-purpuric looking skin lesions reflected extramedullary hematopoiesis with ultrastructural study disclosing evidence of both erythro- and granulopoietic lineage. For the first time, we were able to demonstrate that complexes of red cells in various stages of maturation can occur in the skin, similarly to the erythroblastic islands of the bone marrow. In the pathogenesis of extramedullary hematopoiesis, mechanisms underlying the reconstitution of blood cells must be considered. These may reactivate hematopoiesis in organs where it previously occurred in embryonic and fetal life. Possible causative factors may be great compensatory demand, deficient replacement, or loss or dysfunction of corpuscular blood elements. This would explain the occurrence of this disease entity in conjunction with etiologically completely heterogeneous systemic diseases.