'Mu' heavy chain type 'non-excretory' myeloma

An unusual case of 'non-excretory' myeloma is described in which, using immunofluorescence, only 'mu' heavy chains were detected in almost all bone marrow plasma-cell cytoplasm. Cytoplasmic light chains were completely lacking, and neither monoclonal whole immunoglobulin (Ig) nor free heavy nor light chains were detected in serum and urine, although the clinical and morphological features showed the classical pattern of myeloma. The possible mechanism which could play a role in the disturbance of the Ig-chain secretion observed in this case is discussed.