Thymic changes in histiocytosis.

In order to arrive at a hypothesis of the pathogenesis of thymic changes in histiocytosis, the thymus glands from thirty-two children with histiocytosis were studied. In general, the changes were a severe loss of cortical and medullary structures rather than stress type changes in which only the cortical structure changes. The thymic changes were then classified into three main groups: severe dysplasia equivalent to that seen in congenital immune deficiency, severe nonspecific involution, and a third group designated as a dysmorphic type which resembled those with dysplasia, but, in addition, showed smaller lobules and interstitial histiocytic infiltration. The thymic changes correlated with the type of histiocytic disease. For the purposes of this study, the disease was categorized as Type I or Type II, as previously described. Dysplastic changes were only seen in those patients with Type I histiocytic disease, while involution occurred in patients with Type II histiocytic disease. Dysmorphic change was apparent in both, but it had a much higher incidence in Type II.