Microscopical examination

Bone marrow samples are examined under a high-powered light microscope to detect compositional abnormalities. Cells are stained with a dye so that their morphological features can be visualised.

In myeloma, the main purpose of examining a bone marrow sample is to determine the percentage of myeloma cells present. Myeloma cells can sometimes be distinguished from normal plasma cells because of changes such as low amount of cytoplasm in the cell, they may have more than one nucleus with excessive chromatin staining or may have very prominent nucleoli (see arrows in Figure 3).

Patients who have greater than 10% plasma cells in their bone marrow meet the criteria for a diagnosis of a plasma cell disorder but the exact nature will depend on other parameters and the presence or absence of symptoms (see ‘Differential diagnosis’ section later).

A trephine biopsy can be stained with antibodies to Ig heavy or light chains to demonstrate their presence in the plasma cells and confirm that the plasma cells are monoclonal. This can be a useful for diagnosis if the increase in the number of plasma cells is minimal. A special stain, known as Congo Red, can be used to detect the presence of AL amyloidosis in the bone marrow.