Changes in hemostasis and other disorders caused by monoclonal immunoglobulin and/or free light chains

BACKGROUND: Monoclonal immunoglobulin and/or free light chains cause diverse complications that can affect almost all tissues or organs. AIM: Monoclonal immunoglobulin can interfere with hemostasis and cause both hypercoagulation or hemorrhagic diathesis. In patients with non-malignant gammopathy and untreated multiple myeloma, thrombotic complications are more common than hemorrhagic complications. Exceptionally, monoclonal immunoglobulin can also exhibit the properties of an autoantibody and cause diverse organ damage. Among the more common forms, there is cold agglutinin disease, neuropathy, and various forms of eye damage. In the text, less common disorders are also mentioned. CONCLUSION: All the complications described in the text may be caused by monoclonal immunoglobulin, but they can also have other causes. If it is possible to establish an etiopathogenetic connection of these problems with monoclonal immunoglobulin, then targeted treatment that suppresses its production may lead to the disappearance of the problem.