What is the pathophysiology of eosinophilic granuloma (histiocytosis X)?

Updated: Mar 29, 2018
  • Author: Eleanor M Summerhill, MD, FACP, FCCP; Chief Editor: Zab Mosenifar, MD, FACP, FCCP  more...
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Answer

Pulmonary Langerhans cell histiocytosis X (PLCH) is histologically characterized by parenchymal infiltration of the lungs by activated Langerhans cells. Langerhans cells are differentiated cells of the dendritic cell system and are closely related to the monocyte-macrophage line. These antigen-presenting cells are normally found in the skin, reticuloendothelial system, heart, pleura, and lungs. They may be identified by immunohistochemical staining or by the presence of Birbeck granules via electron microscopy.

PLCH is similar to pediatric histiocytic disorders (Letterer-Siwe disease and Hand-Sch ü ller-Christian disease). However, in contrast to pediatric histiocytoses, which involve multiple organs, PLCH usually manifests in a single organ—the lung. About 4-20% of patients with PLCH also have cystic lesions in the bones. Other organ systems are only rarely affected. [2]

The accumulation of Langerhans cells in the lungs is hypothesized to occur in response to exposure to cigarette smoke. Supporting this hypothesis is the finding that the initial histologic and radiographic findings are peribronchiolar. In addition, the disease is most prominent in the upper and middle lung zones, as seen in other smoking-related lung diseases. The granulomatous infiltrates seen in PLCH are composed of Langerhans cells, eosinophils, lymphocytes, macrophages, plasma cells, and fibroblasts, which form nodules centered on the terminal and respiratory bronchioles, causing destruction of the airway walls. In late stages of the disease, fibrotic stellate scarring occurs, and end-stage PLCH is characterized by this scarring along with cystic spaces and honeycombing.


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