Investigation and diagnosis

• Perform investigations listed for MM (fflp273).

• Serum protein electrophoresis with immunofixation and densitometry to detect, characterise and quantitate paraprotein levels: IgG 66%; IgA 20%; IgM 10%; biclonal 1%; light chain 1%; median ~15g/L.

• Urine electrophoresis: identifies only low levels of Bence Jones proteinuria (generally <1g/24h).

• Stable paraprotein and other parameters on prolonged observation.

• Immunoglobulin quantitation: by nephelometry; only 25% have immuneparesis of uninvolved Ig classes (cf. myeloma).

• Serum ^-microglobulin levels normal (unless renal impairment).

• BM aspirate: <10% plasma cells in BM; median ~5%.

• BM cytogenetics: normal by conventional techniques but all abnormalities in MM described in MGUS by FISH; del(13), t(4;14), ras mutations, p16 and p53 inactivation less common.

• BM trephine biopsy: no evidence of diffuse plasma cell infiltration or osteoclast erosion of trabeculae.

• FBC: no anaemia or other cytopenia except due to unrelated causes.

• Serum chemistry: no hypercalcaemia or unexplained renal impairment.

• Skeletal radiology: no evidence of lytic lesions or pathological fracture; osteoporosis may co-exist from other causes e.g. post menopausal females.

• Other imaging: not routine; MRI of the spine; FDG-PET and 99mTc-MIBI scan are negative in MGUS.

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