Monoclonal Gammopathy of Undetermined Significance

Background

MGUS stands for monoclonal gammopathy of undetermined significance. By definition, there can be no evidence of plasma cell myeloma, amyloidosis, lymphoma or leukemia, or any disorder that may cause a monoclonal gammopathy. The importance of this diagnosis lies in the risk of progressing to a malignancy such as multiple myeloma. Patients are usually at an advanced age but there are no known disease associations.

SYNONYMS Benign monoclonal gammopathy

INCIDENCE 3% of patients over 70 years of age

AGE-RANGE AND MEDIAN Peak in 8th decade
Rare <40 yrs

SEX (MALE:FEMALE) 60% male

GEOGRAPHIC DISTRIBUTION Twice as common in Blacks

PATHOGENESIS CHARACTERIZATION

Cytogenetics No abnormalities

LABORATORY/RADIOLOGIC/OTHER TESTS CHARACTERIZATION

Monoclonal protein by serum protein electrophoresis 95% <3 g/dL
IgM in 67-75% of cases

HISTOLOGICAL TYPES CHARACTERIZATION

Bone marrow biopsy and aspirate Plasma cells should be <5% with a median of 3%
Cytologically, very little atypia of the plasma cells
Plasma cells usually evenly scattered throughout the marrow

SPECIAL STAINS/IMMUNOPEROXIDASE/OTHER CHARACTERIZATION

Immunoperoxidase staining for light chains Light chain ratio less than 16:1 in >90% of cases

DIFFERENTIAL DIAGNOSIS KEY DIFFERENTIATING FEATURES

Multiple myeloma

PROGNOSIS AND TREATMENT CHARACTERIZATION

Prognostic Factors
About 17% develop a malignant lymphoplasmacytic disease at 10 years and 33% develop at 20 years

Patients with IgM and IgA MGUS more likely to progress to malignancy

Increasing size of the serum monoclonal protein spike is the most reliable parameter for predicting progression

Progression of Disease

Percentage

Plasma cell myeloma

66%

Macroglobulinemia

12%

Amyloidosis

14%

Lymphoma or chronic lymphocytic leukemia

8%

Treatment Observation unless evolution to multiple myeloma has occurred

Atlas of Tumor Pathology-Tumors of the Bone Marrow. Volume 9, Third Series. AFIP Press. 1994.

Commonly Used Terms

Hematologic-Lymphatic Diseases

Multiple myeloma

Last Updated 4/1/2001

SYNONYMS	Benign monoclonal gammopathy
INCIDENCE	3% of patients over 70 years of age
AGE-RANGE AND MEDIAN	Peak in 8th decade Rare <40 yrs
SEX (MALE:FEMALE)	60% male
GEOGRAPHIC DISTRIBUTION	Twice as common in Blacks

PATHOGENESIS	CHARACTERIZATION
Cytogenetics	No abnormalities

LABORATORY/RADIOLOGIC/OTHER TESTS	CHARACTERIZATION
Monoclonal protein by serum protein electrophoresis	95% <3 g/dL IgM in 67-75% of cases

HISTOLOGICAL TYPES	CHARACTERIZATION
Bone marrow biopsy and aspirate	Plasma cells should be <5% with a median of 3% Cytologically, very little atypia of the plasma cells Plasma cells usually evenly scattered throughout the marrow

SPECIAL STAINS/IMMUNOPEROXIDASE/OTHER	CHARACTERIZATION
Immunoperoxidase staining for light chains	Light chain ratio less than 16:1 in >90% of cases

DIFFERENTIAL DIAGNOSIS	KEY DIFFERENTIATING FEATURES
Multiple myeloma

PROGNOSIS AND TREATMENT	CHARACTERIZATION
Prognostic Factors	About 17% develop a malignant lymphoplasmacytic disease at 10 years and 33% develop at 20 years Patients with IgM and IgA MGUS more likely to progress to malignancy Increasing size of the serum monoclonal protein spike is the most reliable parameter for predicting progression
*Progression of Disease*	*Percentage*
*Plasma cell myeloma*	66%
*Macroglobulinemia*	12%
*Amyloidosis*	14%
*Lymphoma or chronic lymphocytic leukemia*	8%
Treatment	Observation unless evolution to multiple myeloma has occurred