Light microscopic, S-100 immunostaining, and ultrastructural analysis of dermatopathic lymphadenopathy, with and without associated mycosis fungoides.

Thirty-five patients with dermatopathic lymphadenopathy, 12 with (9 patients and 3 follow-up) and 23 without associated mycosis fungoides, and 7 controls with 26 lymph nodes were studied by light microscopic examination and immunostaining for S-100 protein. Fourteen of these cases were examined ultrastructurally. The group of cases studied included lymph nodes obtained at postmortem examination from three patients with mycosis fungoides and evidence of nodal involvement by light microscopic examination. Lymph nodes from patients with dermatopathic lymphadenopathy and paracortical hyperplasia (but no effacement of architecture by recognizable mycosis fungoides cells by light microscopic examination) associated with biopsy-proven mycosis fungoides showed well-defined, diffusely distributed sheets of S-100-positive cells. Cases of dermatopathic lymphadenopathy unassociated with a skin lymphoma (23 cases), with the exception of 3 cases (12.5%), only showed scattered S-100-positive cells, a similar pattern to that noted in normal or reactive lymph nodes from the control cases and reported literature. In the three cases with diffuse sheets without associated mycosis fungoides, the intensity of S-100 staining was the same in germinal centers as in parafollicular areas, while in cases associated with mycosis fungoides, the staining was predominantly in parafollicular zones. Ultrastructural immunolabeling for S-100 protein also revealed different patterns in both subsets of patients. Interestingly, in cases in which the lymph nodes were identified by light microscopic examination to be replaced by mycosis fungoides, the sheets of S-100-positive cells disappeared. The corresponding ultrastructural evaluation showed cellular aggregates with features of T-cells. A combination of S-100 immunocytochemistry and morphologic ultrastructural assessment can be of help in evaluation of lymphadenopathy in patients with mycosis fungoides. Although this study indicates that the finding of sheets of S-100-positive cells in patients with dermatopathic lymphadenopathy is not always associated with mycosis fungoides, the identification of diffuse sheets of S-100-positive cells, especially with parafollicular distribution, in a patient without known T-cell lymphoma should probably be considered an indication to suggest a complete clinical evaluation to rule out the possibility of an undiagnosed mycosis fungoides. The finding of sheets of S-100-positive cells in patients with proven mycosis fungoides may be a morphologic indicator of impending extracutaneous dissemination.