Tissue necrosis caused by distal capillary thrombosis resulting from cryoglobulin precipitation in the vessels. The black tissue under the nails is ischemic, and will eventually slough, or be reabsorbed by the body.
Review Date 2/8/2017
Updated by: Gordon A. Starkebaum, MD, Professor of Medicine, Division of Rheumatology, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.