Pathologists and pediatric hematologist/oncologists of the World Health Organization's Committee on Histiocytic/Reticulum Cell Proliferations and the Reclassification Working Group of the Histiocyte Society present a classification of the histiocytic disorders that primarily affect children. Nosology, based on the lineage of lesional cells and biological behavior, is related to the ontogeny of histiocytes (macrophages and dendritic cells of the immune system). Dendritic cell‐related disorders of varied biological behavior are dominated by Langerhans cell histiocytosis, but separate secondary proliferations of dendritic cells must be differentiated. Juvenile xanthogranuloma represents a disorder of dermal dendrocytes, another dendritic cell of skin. The hemophagocytic syndromes are the most common of the macrophage‐related disorders of varied biological behavior. Guidelines for distinguishing the exceedingly rare malignant diseases of histiocytes from large cell lymphomas through the use of a battery of special studies are provided. Med. Pediatr. Oncol. 29:157–166, 1997. © 1997 Wiley‐Liss, Inc.

PCR offers a rapid, sensitive diagnostic method for myocardial viral infection. While enterovirus is an important etiological agent, adenovirus was more prevalent in this series and should be evaluated when etiology is sought. PCR used in conjunction with standard endomyocardial biopsy appears to enhance the likelihood of detecting viral genome in the myocardium of patients with clinical evidence of myocarditis.

Thrombocytopenia-associated multiple organ failure (TAMOF) is a poorly understood syndrome in critically ill children. ADAMTS-13, formerly known as von Willebrand factor (VWF) cleaving protease, is decreased in adults with VWF mediated thrombotic microangiopathy, and intensive plasma exchange (PEx) both replenishes ADAMTS-13 and improves outcome in these patients. We hypothesized that children with TAMOF syndrome have decreased ADAMTS-13 activity which can be replenished with PEx. In the first of two consecutive studies, relationships between platelet count, VWF multimers, ADAMTS-13 activity, plasminogen activator inhibitor-1 (PAI-1) and prothrombin time (PT) were analyzed in children with and without TAMOF. In the second study, children with severe TAMOF (platelet counts<100,000/mm3 and ≥3 organ failure) were randomized to PEx or standard therapy. In the first study, children with TAMOF (n=28) had decreased ADAMTS-13 activity, but similar PAI-1 activity and PT compared to children with MOF without thrombocytopenia (n=9) (p<0.05). All non-survivors (n=7) had TAMOF, reduced ADAMTS 13 activity, and VWF-rich microvascular thromboses at autopsy. In the second study, PEx (n=5, median 12 days, 4–28 days) restored ADAMTS-13 activity and organ function, compared to standard therapy (n=5) (p<0.05). Children with TAMOF syndrome can have VWF mediated thrombotic microangiopathy. Similar to adult experience, PEx can replenish ADAMTS-13 activity and reverse organ failure in these children.