Cytomorphology of Langerhans cell histiocytosis

To determine the diagnostic accuracy in recognizing Langerhans cell histiocytosis (LCH) in cytologic smears obtained between 1977 and 1994 and to analyze the composition of these smears and thus identify various cytomorphologic patterns.

The study group consisted of 37 cytologic smears (34 patients) taken from 30 bone lesions, 5 lymph nodes, 1 parotid gland and 1 conjunctival lesion. We noted the presence of various components in each smear and estimated their abundance. Immunocytochemical staining for S-100 protein was performed in seven cases.

LCH was recognized in 22 cases, suspected in 5 and unrecognized in 1; one case was suspected of malignancy. Six smears were nondiagnostic. Three reactive lesions were misinterpreted as LCH. Smears contained numerous Langerhans cells (LCs), eosinophils, neutrophils, lymphocytes, macrophages and multinucleated giant cells. Some capillary fragments were usually present. The morphology of smears varied somewhat in the percentage of individual constituents present as well as in the appearance of the LCs. Immunocytochemical staining for S-100 protein was positive in six cases and equivocal in one.

The cytomorphologic pattern of LCHs in fine needle aspiration biopsy smears is usually characteristic, and a correct diagnosis is possible, especially with the aid of immunocytochemistry. One must be aware, however, of different morphologic patterns of LCHs and of unusual appearances of LCs, which may lead to diagnostic errors.