Lessons From the Friday Unknowns
The biopsy specimen shows lymph node with somewhat preserved architecture.
The paracortical regions are expanded by numerous histiocytes, plasmacytoid dendritic cells and small lymphocytes with many apoptotic cells. No granulocytes are observed.
The uninvolved lymph node shows preserved B-cell and T-cell regions.
The expanded paracortical regions are composed of many CD68+ histiocytes and many T-cells positive for CD3, CD5, CD7 and CD8. The antibody specific for CD4 highlights T-cells (less than CD8+ cells) and many histiocytes. The antibody specific for granyzme B shows many cytotoxic lymphocytes in these regions. The BCL-2 antibody is either negative or weakly positive in lymphocytes and histiocytes. Very few B-cells are present in the paracortical regions as shown by antibodies specific for CD20, VCD79A and PAX-5. The antibody specific for CD30 highlights few immunoblasts. CD10, CD15, CD56, CD57, BCL-6, MUM1/IRF4, ALK1, and antibodies specific for CMV, HSV, and spirochetes are negative.
The antibody specific for Ki-67 highlights many proliferating cells in the paracortical regions.
Flow cytometry immunophenotypic studies performed elsewhere showed a mixture of T-cells and polytypic B-cells. There is no support for lymphoma.
Molecular studies using PCR methods showed no evidence of clonal TRG rearrangements (polyclonal smear pattern) and a minor clonal TRB rearrangement superimposed on a polyclonal smear pattern.
In summary, These findings support the diagnosis of Kikuchi-Fujimoto lymphadenitis. In our experience, very small T-cell clones can occur in cases of Kikuchi-Fujimoto lymphadenitis.
Link to digital slides: https://bit.ly/3fYAycc | Slides labeled case 3