Intracellular immunoglobulin distribution of bone marrow plasma cells as a diagnostic aid for primary amyloidosis

Analysis of plasma cell clonality in localized AL amyloidosis

AL amyloidosis is characterized by fibrillar tissue deposits composed of monoclonal immunoglobulin light chains(IgLs). It has been speculated that clonal expansion of plasma cells may occur locally and produce amyloidogenic IgLs. Both immunohistochemistry and molecular genetics are useful for examining plasma cell clonality from paraffin-embedded tissue sections, which are easy to obtain. We evaluated plasma cell clonality in 16 biopsy cases of localized AL amyloidosis using these two methods. A clonal excess of plasma cells was detected in 6 (37.5%) cases immunohistochemically, in 10 (62.5%) cases molecularly, and in 13 (81.3%) cases by at least one of the two methods. These results support local synthesis of the light chain proteins in localized AL amyloidosis.

IgM demyelinative neuropathy with amyloidosis and biclonal gammopathy

A 59-year-old man developed a sensorimotor neuropathy of the upper and lower limbs, associated with a biclonal gammopathy, within the space of a few months. Each of two paraproteins was coupled with a distinct IgM kappa IgG lambda light chain. Examination of a nerve biopsy specimen by electron microscopy revealed a demyelinative process with a widening of the interlaminar space in the myelin sheath, as well as deposits of amyloid substance between nerve fibers. Direct immunofluorescence revealed the presence of IgM and of the kappa light chain in certain Schwann cells, while the lambda IgG was fixed to the amyloid deposits. Immunoperoxidase histochemistry showed a positive reaction in normal human nerve tissue to the immune serum IgM and kappa light chain. The findings suggest that the widening of the interlaminar space of the diseased myelin corresponds to an active fixation of immunoglobulin on the sheath of the Schwann cell. The presence of two light chains in this patient's gammopathy caused a dual pathology: the kappa chain, a demyelinative neuropathy, and the lambda chain, a primary amyloidosis, with deposits in the peripheral nerve and in the kidney.

Primary cardiovascular amyloidosis with benign monoclonal gammopathy

A 54-year-old woman is reported whose primary amyloidosis was diagnosed at autopsy. Amyloid deposits were found in the myocardium, the striated muscles, the smooth muscle layers of the gut and the wall of the blood vessels. The deposits showed resistance to induced proteolysis. A large number of mature plasma cells was demonstrated in the bone marrow, and immunocytochemical studies revealed a considerable increase in the proportion of plasma cells which were positive for kappa light chains of immunoglobulins, indicating a monoclonal gammopathy. This view was strongly supported by the unexpected finding that amyloid deposits were positive for kappa light chains. The relationship between the kappa positive reaction of amyloid and its resistance to induced proteolysis are discussed.