Monoclonal Gammopathy of Undetermined Significance (MGUS)

What is this term Monoclonal Gammopathy of Undetermined Significance (MGUS)

Monoclonal gammopathy of undetermined significance is a condition in which there is too much of a protein called monoclonal protein, or M protein, in the blood. MGUS can cause you to have too many cells in your blood and not enough space for healthy cells. This condition may increase your risk of developing multiple myeloma or other blood disorders in the future.

7 Interesting Facts of Monoclonal Gammopathy of Undetermined Significance

  1. Premalignant clonal plasma cell disorder characterized by presence of serum M protein in persons without any evidence of multiple myeloma, macroglobulinemia, amyloidosis, or other related diseases
  2. Is asymptomatic and is usually diagnosed incidentally on laboratory testing 
  3. Main clinical significance is the lifelong risk of transformation to myeloma or related malignancy at a fixed but unrelenting rate of about 1% per year
  4. Differentiated from multiple myeloma (and smoldering multiple myeloma) by the concentration of the M protein, the marrow plasma cell percentage, and the presence or absence of anemia, renal failure, hypercalcemia, or lytic bone lesions
    • Defined by a serum M protein level lower than 3 g/dL, less than 10% clonal plasma cells in the bone marrow, and absence of myeloma-defining events 
      • There can be no evidence of anemia, constitutional symptoms, hyperviscosity, lymphadenopathy, or hepatosplenomegaly that can be attributed to the underlying lymphoproliferative disorder
    • Because anemia and renal insufficiency are relatively common in elderly people with monoclonal gammopathy of undetermined significance, investigate the causes of these conditions carefully with adequate laboratory testing
      • Only patients with strong evidence of end-organ damage thought to be directly related to a plasma cell disorder can be considered to have active multiple myeloma
    • Variants of monoclonal gammopathy of undetermined significance are the IgM form, the non-IgM form, and the light chain form
  5. MRI is not required in all patients routinely to evaluate monoclonal gammopathy of undetermined significance
  6. Patients with the IgM form are at risk of progression to Waldenström macroglobulinemia, whereas patients with the non-IgM form or the light chain form are at risk of progression to active multiple myeloma
  7. Specific risk factors that predict disease progression include the following: 
    • Abnormal serum free light chain ratio
    • Non-IgG form of monoclonal gammopathy of undetermined significance
    • High serum level of M protein (15 g/L or more)

What are the causes?

The exact reason of this condition is unknown.

What increases the risk?

You are more likely to develop this condition if:

  • You are African American.
  • You are age 50 or older.
  • You are male.
  • You have an autoimmune disease.
  • You have been exposed to radiation.
  • You have a family history of MGUS.

What are the signs or symptoms?

There are no symptoms of this condition.

How is this diagnosed?

This condition may be diagnosed with a blood test that checks for M protein.

How is this treated?

Treatment for this condition may involve:

  • Having regular exams. This will help your physician to monitor your health.
  • Having tests done regularly, such as:
    • Blood tests to check for M protein in your body.
    • Imaging tests, such as a CT scan.
    • Bone marrow biopsy. This is the test where a sample of bone marrow is taken from your body and examined under a microscope.

Follow these instructions at home:

  • Keep all follow-up visits as told by your health care provider. This is important.

Contact a health care provider if:

  • You have trouble swallowing.
  • You have pain in your back or ribs.
  • You have a fever.
  • You are bruising easily.

Get help right away if:

  • You break a bone.
  • You have trouble breathing.

Take Home points

  • Monoclonal gammopathy of undetermined significance is a disorder in which there is too much of a protein called monoclonal protein, or M protein, in the blood.
  • This condition may be diagnosed with a blood test that checks for M protein.
  • Treatment for this condition may involve having tests done regularly. Diagnosis includes blood tests, imaging tests, and a bone marrow biopsy.
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