image

25.2.3. Definition of monoclonal gammopathy of undetermined significance

Chapter 25

The MM guidelines [42] also summarise the current definitions of monoclonal gammopathy of undetermined significance (MGUS) (Chapter 13) and these are listed below (Table 25.2):

MGUS type Definition (all criteria must be met)
Non-IgM MGUS

▪ Serum monoclonal protein (non-IgM type) <30 g/L

▪ Clonal bone marrow plasma cells <10%

▪ Absence of end-organ damage (such as hypercalcaemia, renal insufficiency, anaemia and bone lesions [CRAB features]) or amyloidosis that can be attributed to the plasma cell proliferative disorder

IgM MGUS

▪ Serum IgM monoclonal protein <30 g/L

▪ Bone marrow lymphoplasmacytic infiltration <10%

▪ No evidence of anaemia, constitutional symptoms, hyperviscosity, lymphadenopathy, hepatosplenomegaly, or other end-organ damage that can be attributed to the underlying lymphoproliferative disorder

Light chain MGUS

Abnormal FLC ratio (<0.26 or >1.65)

Increased level of the appropriate involved light chain (increased κ sFLCs in patients with ratio >1.65, and increased λ sFLCs in patients with ratio <0.26)

▪ No immunoglobulin heavy chain expression on immunofixation

▪ Absence of end-organ damage (such as CRAB features) or amyloidosis that can be attributed to the plasma cell proliferative disorder

▪ Clonal bone marrow plasma cells <10%

▪ Urinary monoclonal protein <500 mg/24 hours

Table 25.2. Categories of MGUS [42]. CRAB: hypercalcaemia, renal insufficiency, anaemia, bone lesions.