There are four monoclonal gammopathies
- Monoclonal gammopathy of uncertain significance (MGUS) defined as monoclonal component <3g/dL and bone marrow plasma cells less than 10% and no end organ damage.
- Asymptomatic myeloma defines as monoclonal component ≥ 3g/dL and/or bone marrow plasma component ≥10% in the absemce of end organ damage.
- Multiple myeloma Bone marrow plasma cells ≥ 10% in the presence of end organ damage attributable to the plasma cell proliferation.
- Solitary plasmacytoma which may be further divided into osseous and non-osseous solitary plasmacytoma.
End organ damage includes
- Osteolytic lesions
- Anaemia defined as fall in haemoglobin by more than 2g/dL below normal or a haemoglobin < 10g/dL
- Renal failure defined as serum creatinine >2mg/dL and and estimeted creatinine clearance <40 ml/min.
- Hypercalcaemia defined as serum calcium > 11.5g/dL.
Osteolytic lesions are most commonly assessed by a skeletal survey. The skeletal survey in patients with multiple myeloma includes
- Frontal and lateral view of the skull
- Frontal and lateral views of the cervical, thoracic and lumbar spine
- A coned-down frontal view of the dens axis
- Frontal views of the rib cage
- Frontal Views of both humeri
- Frontal Views of both femora
- Frontal Views of both knees
- Frontal Views of the pelvis.
About 80% of the patients with multiple myeloma have lesions apparent on skeletal survey. Vertebrae are involved in 66%, ribs in 45%, skull in 40%, pelvis in 30% and long bones in 25%. Other estimates have put the involvement at spine 49%, skull 35%, pelvis 34%, ribs 33%, humori 22%, femora 13% and mandible 10%. The figures may differ from report to report but it is clear that the axial skeleton and proximal long bones are the commonest sites of involvement in myeloma. These correspond to areas of active marrow in an adult. The utility of conventional radiology in evaluation of multiple myeloma is limited by the fact that al least 30-50% of the bone must be lost for the lytic lesions to be visible. Myeloma cell origin protein DKK1 results in loss of cells of stem cells of the osteoblastic lineage. The osteolytic lesions of multiple myeloma may not heal despite treatment. Skeletal survey is not only important for diagnosis. There is an association between number of lytic lesions and tumour load. Number of lytic lesions determines stage by the Durie-Salmon criteria but is not needed for the international staging system.
The images show lytic lesions observed in patients with multiple myeloma.