S-100 staining in the diagnosis of eosinophilic granuloma of lung

The authors used immunohistochemical staining for S-100 protein to search for Langerhans cells in 7 cases of pulmonary eosinophilic granuloma (EGL) and in 18 cases of other pulmonary processes (including reactive eosinophilic pleuritis, chronic interstitial pneumonias, eosinophilic pneumonia, and nonspecific scars), which can produce diagnostic confusion with EGL. Qualitatively, Langerhans cells were found in almost every disease. However, cases of active or resolving EGL showed greater than 75 such cells/10 high-power fields (hpf), often appearing as densely packed aggregates (a virtually diagnostic feature), while all other conditions, including completely scarred EGL, showed fewer than 35 Langerhans cells/10 hpf, and the cells were scattered through the parenchyma. The authors conclude the following: (1) Langerhans cells participate in many types of inflammatory process in the lung, and hence the mere presence of Langerhans cells is not diagnostic of EGL; (2) S-100 staining with quantitation of Langerhans cells is a useful adjunct in the diagnosis of active and resolving EGL.