Comparison of bone marrow sections, smears and immunohistological staining for immunoglobulin light chains in the diagnosis of benign and malignant plasma cell proliferations.

Bone marrow specimens from 118 patients with clinical suspicion of multiple myeloma were studied to assess the diagnostic reliability of histological and cytological criteria. Plasma cell clonality was assessed by demonstrating light chain restriction. In most cases of multiple myeloma, the classical cytological and histological criteria were found. In eight cases in which the marrow contained less than 10% of plasma cells, there was discordance between the light microscopic and immunohistochemical findings. In six cases without evidence of multiple myeloma and with polyclonal plasma cells in bone marrow, abnormal plasma cells resembling a malignant proliferation were found. These findings indicate that comparison of histological and cytological results with immunohistological studies for immunoglobulin light chains in bone marrow biopsy sections can be helpful in the evaluation of patients with a suspicion of multiple myeloma and when the marrow contains less than 10% of plasma cells.