Intracytoplasmic filamentous inclusions in the peripheral blood of a patient with chronic lymphocytic leukemia. A bright-field, electron microscopic, immunofluorescent, and flow cytometric study.

Intracellular inclusions in lymphoproliferative disorders are not common. Multiple different types of inclusions have been reported in chronic lymphocytic leukemia (CLL), including vacuoles, crystals, and pseudocrystals. Most of the reported cases were seen in the bone marrow lymphocytes, and the majority of these on electron microscopy. We report a case of long-standing CLL with no therapy that had filamentous cytoplasmic inclusions in the peripheral blood that were readily seen by light microscopy. Electron microscopy demonstrated dilated cisternae of the rough endoplasmic reticulum filled with amorphous electron-dense material. By immunofluorescence, the material proved to be immunoglobulin G-lambda deposits. The immunophenotype had the typical CLL pattern with positive staining with CD19, CD5, and CD23, and low-density CD20 staining; however, it also had unusual staining with CD25 and intermediate-intensity staining with CD22.