Waldenstrom macroglobulinemia is a chronic, slow-growing lymphoproliferative disorder. It usually affects older adults and is primarily found in the bone marrow, although lymph nodes and the spleen may be involved. Affected individuals have a high level of an antibody called immunoglobulin M (IgM) in their blood, which can cause thickening of the blood (hyperviscosity). Although some individuals initially do not have symptoms and are diagnosed from routine blood work, common symptoms may include weakness, appetite loss and weight loss. Other symptoms may include peripheral neuropathy, fever, Raynaud's phenomenon, and mental status changes. Hyperviscosity of the blood may cause nosebleeds, headaches, dizziness, and blurring or loss of vision. The cause of the condition is not known but environmental, genetic, and viral factors have been suggested. There have been some reports of familial cases suggesting a genetic predisposition.