Restrictive cardiomyopathy with kappa light chain deposits in myocardium as a complication of multiple myeloma. Histochemical and electron microscopic observations.

kappa Light chain deposits occurring in myocardium as a complication of multiple myeloma were identified ultrastructurally and immunohistochemically in a right ventricular endomyocardial biopsy specimen from a patient who presented with clinical and hemodynamic findings of restrictive cardiomyopathy. These deposits were not evident on routine histopathologic examination; they were Congo red-negative and gave a positive immunoperoxidase reaction for kappa light chains and a negative reaction for lambda chains. They consisted of amorphous, electron-dense granules that formed discontinuous layers adjacent to the plasma membranes of cardiac myocytes, arteriolar endothelial and smooth-muscle cells, and neural elements. These observations underscore the need for critical study of endomyocardial biopsy specimens, using electron microscopy and immunohistochemical reagents, for the precise identification of protein components in tissue deposits in patients suspected of having cardiac amyloidosis or related disorders.