Localized thymic Langerhans' cell histiocytosis and its relationship with myasthenia gravis. Immunohistochemical, ultrastructural, and cytometric studies.

OBJECTIVE: It has been suggested that localized Langerhans cell histiocytosis may represent an exaggerated form of a proliferative process that has been reported in a few patients with myasthenia gravis. To evaluate the relationship between thymic Langerhans' cell proliferation and myasthenia gravis, we analyzed a rare case of localized thymic Langerhans' cell histiocytosis and examined thymic Langerhans' cell distribution in myasthenic and control patients.
DESIGN: Immunohistochemical, ultrastructural, and image cytometric DNA analyses were performed on the index case. Immunostaining for S100 was performed on 20 additional thymuses, 10 from patients with myasthenia gravis and 10 from control patients.
RESULTS: Immunohistochemical studies revealed no increase in Langerhans' cells in the surrounding thymic tissue of the index case. No difference was found between the number of Langerhans' cells in the remaining thymuses of myasthenia patients compared with the control group, and no micronodular proliferations were identified in either group.
CONCLUSIONS: Localized thymic Langerhans' cell histiocytosis is an unusual lesion that is associated with myasthenia gravis in some patients. In the few cases reported at present, however, the lesion does not appear to be related pathogenetically to myasthenia gravis.