Mycosis fungoides: An ultrastructural study

Ultrastructural observations were carried out on skin, lymph nodes, spleens, and peripheral blood of 19 patients in whom a clinical and pathologic diagnosis of mycosis fungoides was made. Skin sections of 15 patients revealed atypical cells with varying degrees of nuclear indentation ranging from slightly indented to highly convoluted or „cerebriform” types. In each case they were observed either singly, in clusters, or both. The ultrastructure of the atypical cells in 5 lymph nodes, 4 spleens, and 5 peripheral blood samples was similar. The majority of these cells was larger than lymphocytes, but smaller than histiocytes. In one skin biopsy, emperipolesis of an atypical cell was noted. The only extracutaneous neoplastic disease in which more than occasional cells with convoluted nuclei morphologically similar to those found in mycosis fungoides were seen was poorly differentiated lymphocytic lymphoma with a nodular (follicular) pattern. No such cells were observed in malignant lymphoma of the poorly differentiated lymphocytic type without nodular pattern. An occasional cell with irregular nuclear configuration was present in 9 reactive lymph nodes and 24 histologically „normal” spleens of patients without any malignant disease. Our electron microscopic findings suggest: 1) that the presence of cells with varying degrees of nuclear indentations and convolutions is characteristic of mycosis fungoides only when they occur in clusters or sheets; and 2) that the atypical cells of mycosis fungoides are most likely to be of lymphocytic origin.