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Perth Haematology :: Dr Steven Ward

Myeloma and Plasma Cell Disorders

 

Consensus Statement (BJH 2010)

 

MGUS  :: Monoclonal Gammopathy of Uncertain Significance

MGUS refers to a situation where extra antibody protein is present in the blood without an obvious underlying cause for the extra antibody protein.

 

Normal antibody production

The marrow contains cells of the immune system called plasma cells. Plasma cells produce antibodies. Plasma cells are responsible for the immunity to common infections. A few plasma cells are programmed to recognise a particular bacteria and produce small amounts of antibody that can lead to the killing of the specific bacteria. Normally there is a small amount of many different antibodies in circulating in the blood, having been made by many different plasma cells.

 

Abnormal antibody production

In some situations the plasma cells become malignant tumour cells and do not behave normally. Increased numbers of identical plasma cells are made and these all produce the same antibody, in large amounts. Often the antibody has no useful function (ie does not recognise bacteria). Increased amounts of one specific antibody is termed a monoclonal antibody or paraprotein. This is the case in Multiple Myeloma or some forms of lymphoma.

 

MGUS

In MGUS there is extra antibody but NO evidence of an underlying cause for the extra antibody. There is no excess of plasma cells therefore no myeloma. There is a monoclonal paraprotein, but this is usually relatively small and often remains stable over time. 

 

MGUS is therefore a diagnosis of exclusion of the other causes of a monoclonal paraprotein mainly myeloma and lymphoma.

 

MGUS DIAGNOSIS

#

Criteria all 3 required

1

Low level of serum/urine paraprotein: IgG <30g/L, IgA <20g/L K or L < 1.0g/24hr

2

Monoclonal marrow plasma cells <10%

3

Normal Ca2+, Hb, creatinine

No bone lesions on skeletal survey / other imaging

No clinical or laboratory features of amyloidosis or light-chain disease

 

Features

MGUS is often a chance finding, when tests are done to investigate something else. It does not cause any symptoms or problems itself.

MGUS becomes progressively more common with age: affecting 1% of 60 year-olds and up to 10% of 80 year-olds.

MGUS must be followed-up regularly to ensure the paraprotein level does not rise or new features become evident to suggest progression to myeloma or lymphoma. Up to 20% of patients with MGUS will go on to develop myeloma or lymphoma over a 20 year period. Usually blood tests are monitored along with clinical review once a year.