(See also Overview of Plasma Cell Disorders Overview of Plasma Cell Disorders Plasma cell disorders are a diverse group of disorders of unknown etiology characterized by Disproportionate proliferation of a single clone of B cells Presence of a structurally and electrophoretically... read more .)
The incidence of monoclonal gammopathy of undetermined significance (MGUS) increases with age, from 1% of people aged 25 years to > 5% of people > 70 years. MGUS may occur in association with other disorders (see table Classification of Plasma Cell Disorders Classification of Plasma Cell Disorders 
), in which case M-proteins (monoclonal immunoglobulin proteins, which may consist of both heavy and light chains or of only a light chain) may be antibodies produced in large amounts in response to protracted antigenic stimuli.
MGUS usually is asymptomatic, but peripheral neuropathy can occur, and patients are at higher risk of enhanced bone loss and fractures. Although most cases are initially benign, up to 25% (1%/year) progress to myeloma Multiple Myeloma Multiple myeloma is a cancer of plasma cells that produce monoclonal immunoglobulin and invade and destroy adjacent bone tissue. Common manifestations include lytic lesions in bones causing... read more 
or a related B-cell disorder, such as macroglobulinemia Macroglobulinemia Macroglobulinemia is a malignant plasma cell disorder in which B cells produce excessive amounts of IgM M-proteins. Manifestations may include hyperviscosity, bleeding, recurring infections... read more , amyloidosis Amyloidosis Amyloidosis is any of a group of disparate conditions characterized by extracellular deposition of insoluble fibrils composed of misaggregated proteins. These proteins may accumulate locally... read more 
or lymphoma Overview of Lymphoma Lymphomas are a heterogeneous group of tumors arising in the reticuloendothelial and lymphatic systems. The major types are Hodgkin lymphoma Non-Hodgkin lymphoma See table Comparison of Hodgkin... read more .
Diagnosis of MGUS is usually suspected when M-protein is incidentally detected in blood or urine during a routine examination. On laboratory evaluation, M-protein is present in low levels in serum (< 3 g/dL) or urine (< 200 mg/24 hours). MGUS is differentiated from malignant plasma cell disorders because M-protein levels are lower and lytic bone lesions, anemia, and renal dysfunction are absent. Because of fracture risk, baseline evaluation with a skeletal survey (ie, plain x-rays of skull, long bones, spine, pelvis, and ribs) and bone densitometry should be done. Bone marrow shows only mild plasmacytosis (< 10% of nucleated cells).
No antineoplastic treatment is recommended. However, recent studies suggest that MGUS patients with associated bone loss (osteopenia or osteoporosis Osteoporosis Osteoporosis is a progressive metabolic bone disease that decreases bone mineral density (bone mass per unit volume), with deterioration of bone structure. Skeletal weakness leads to fractures... read more 
) may benefit from treatment with intravenous bisphosphonates but less frequently than the monthly treatments usually required to treat patients with multiple myeloma Multiple Myeloma Multiple myeloma is a cancer of plasma cells that produce monoclonal immunoglobulin and invade and destroy adjacent bone tissue. Common manifestations include lytic lesions in bones causing... read more . Every 6 to 12 months, patients should undergo clinical examination and serum and urine protein electrophoresis to evaluate for disease progression.
