THE VALUE OF IMMUNOHISTOCHEMISTRY
IN THE ASSESSMENT OF BONE MARROW DISORDERS

Attilio Orazi, M.D., FRCPath. and Dennis P. O'Malley, M.D.

IMMUNOSECRETORY DISORDERS These disorders are diagnosed by a multiparametric approach which includes clinical, radiological, and laboratory data. Bone marrow aspirate and biopsy is used to assess the number, the distribution pattern, and the degree of cytologic differentiation of the plasma cells. In multiple myeloma, the plasma cells usually account for 20% or more of the marrow nucleated cells and frequently appear arranged in cell clusters or large sheets in the bone marrow biopsy. Plasma cell enumeration CD138, which is an optimal marker for plasma cell detection in bone marrow aspirates analyzed by flow cytometry, can be used to identify and enumerate these cells in paraffin embedded bone marrow biopsies. All cases of MM, including plasmablastic and leukemic cases, show strong CD138 immunoreactivity. Conversely, B-cell lymphomas, are usually negative. In lymphoplasmacytic lymphoma (LPC), the plasma cell component expresses CD138 while the lymphocytes are negative. The combination of CD20 positive lymphocytes intermingled with CD138 positive plasma cells is a characteristic findings observed in LPC involved marrows. Light chain restriction Immunohistochemistry for immunoglobulin light chains is generally used to document the presence of a clonal plasma cell population in cases of plasma cell dyscrasia and multiple myeloma. We have found that the assessment of clonality by this technique becomes difficult when the marrow contains less than 5% plasma cells (Wolf et al., 1990). Immunoglobulin heavy chain stainin, which is usually accompanied by a high nonspecific background uptake that makes the interpretation difficult or impossible, is only rarely used. However, heavy chain stains can be useful in cases of heavy chain disease. Other antigens (e.g. CD56, cyclin D1) can be found expressed in myeloma cells (San Miguel et al., 1995). Cyclin D1 has been associated with an aggressive clinical behavior (Hoechtlen-Vollmar et al., 2000). Amyloid can be seen in the bone marrow in various types of immunosecretory disorders. Amyloid is usually demonstrated by its characteristic apple-green birefringence with Congo red staining. The distinction between primary (AL) and secondary (AA) amyloidosis can occasionally be required. The presence of a clonal plasma cell population in the same biopsy in which amyloid is found usually suggests type AL amyloidosis. AL and AA amyloid can be more specifically distinguished by the preincubation of biopsy sections with potassium permanganate followed by Congo red staining. AL amyloid retains its reactivity but Congo red staining of AA is lost. Immunohistochemical techniques can also be used for amyloid typing. Commercially available antibodies reactive with various amyloid fibril proteins in routinely processed sections include anti AL-kappa and lambda, anti AA peptide, transthyretin, beta2-microglobulin, and prealbumin. We have had little experience with these reagents. 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