Monoclonal gammopathies are a group of disorders characterized by proliferation of monoclonal plasma cells, which produce and secrete monoclonal immunoglobulin or fragments of monoclonal immunoglobulin (M protein). This paper proposes to review diagnostic criteria of the most important monoclonal gammopathies and their differential diagnosis, because superposition of many clinical characteristics is common between variants. The monoclonal gammopathy of undetermined significance (MGUS) is defined by the presence of serum M protein < 3g/dL and/or urinary M protein < 1g/24h, bone marrow plasma cell < 10%, and absence of organ and tissue damage. Asymptomatic multiple myeloma (MM) is characterized by the presence of M protein, bone marrow or tissue biopsy plasma cell infiltration, and non-compliance of the criteria for MGUS, symptomatic MM and solitary plasmacytoma. Symptomatic MM is a plasma cell neoplasm associated with serum or urinary M protein, bone marrow or tissue biopsy plasma cell infiltration and related organ or tissue damage: elevated calcium levels, renal insufficiency, anemia and bone lesions. If no M protein is detected (nonsecretory MM), then at least 30% monoclonal bone marrow plasma cell infiltration and/or a biopsy-proven plasmacytoma is required for MM diagnosis. If a solitary (biopsy-proven) plasmacytoma or osteoporosis (without fractures) are the sole defining criteria, then at least 30% plasma cells are required in the bone marrow for MM diagnosis. Monoclonal gammopathies may be associated with many different diseases, including lymphoproliferative disorders, connective tissue disorders, neurologic, dermatologic and infectious diseases. The clinical and laboratorial characteristics should be very well defined in each variant, malign or benign, easily determining the diagnosis of monoclonal gammopathies and then their clinical management.
Monoclonal gammopathies; diagnosis; differential diagnosis
