Light chain crystal deposition as a manifestation of plasma cell dyscrasias: the role of immunoelectron microscopy.

Light chain crystal deposition disease is a rare and poorly characterized entity that can be confused with a number of different conditions, depending on where the disease process is manifested. The present study explored the role of ultrastructural immunogold labeling in the diagnosis of this condition. Seven cases of light chain crystal deposition (kappa light chain-related) are reported. Immunohistochemistry and immunofluorescence techniques play a rather limited role in the evaluation of these cases, as a result of the inability to detect monoclonal kappa light chains in association with the crystalline structures or high background staining. Ultrastructural labeling is the method of choice to fully characterize these cases. However, surgical pathologists must learn to recognize the findings associated with this condition to avoid misdiagnosis. If the diagnosis is at least suspected, then a complete hematologic workup may identify the underlying plasma cell dyscrasia. It must be emphasized that in some patients the plasma cell dyscrasia does not become clinically manifested until years after the diagnosis of light chain crystal deposition.