Bone Marrow Findings Further Support the Hypothesis that Essential Mixed Cryoglobulinemia Type II is Characterized by a Monoclonal B-Cell Proliferation

One-hundred-sixteen consecutive bone-marrow biopsies were taken from 76 patients with essential mixed cryoglobulinemia type II (type II cryo), whose median follow-up was 97 months. Fifty-four out of fifty-six subjects who underwent ELISA and RIBA tests for HCV, were found to be positive. At conventional light microscopic examination, 64/76 patients showed discrete lymphoid infiltrates consisting of small elements with plasmacytoid differentiation and with frequent paratrabecular location. Thirty-nine biopsies were studied by immunohistochemistry that revealed the B-cell nature of the infiltrates (CD20+, CD45RA+, CD79α+, CD3-, CD45RO-), with demonstrable monotypic Ig light-chain restriction in 22 cases. It is worthy of note that the lymphoid elements usually appeared protected against apoptosis, because of the strong expression of the bcl-2 oncogene product, and provided with a very low proliferative capacity, the Ki-67 index being lower that 3%. The latter findings are in keeping with the indolent behavio...