Multiple Myeloma Bone Disease
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Direct answer
Multiple myeloma bone disease is osteolysis caused by clonal plasma cells, which release signals such as RANKL and DKK1 that activate osteoclasts and block osteoblasts. It typically appears as multiple punched-out lytic lesions without a reactive sclerotic rim, in the skull, spine, ribs and pelvis. The CRAB criteria mark the end-organ damage that makes myeloma symptomatic, and lytic bone lesions form one of them.
What you must remember
- Lesions: punched-out lytic lesions without reactive sclerosis, often in the skull, spine, ribs and pelvis.
- Imaging: a skeletal survey detects the lesions better than a bone scan, which is often normal because the lesions are osteolytic. Whole-body low-dose CT or PET-CT is now preferred in many centres.
- Mechanism: RANKL and DKK1 drive osteoclast activation and block osteoblast formation, causing diffuse osteoporosis as well as focal lesions.
- CRAB criteria: hypercalcaemia, renal insufficiency, anaemia and bone lesions define symptomatic disease that needs treatment; current IMWG criteria also add biomarkers such as 60 percent or more marrow plasma cells.
- Diagnosis: clonal marrow plasma cells, usually 10 percent or more, with a serum or urine monoclonal protein; Bence Jones protein is the light chain found in urine.
- Solitary plasmacytoma: a single bone or soft-tissue lesion of clonal plasma cells, treated with radiotherapy, with a risk of progression to myeloma.
- Emergency: vertebral collapse with cord compression needs urgent imaging and specialist management.
- Bone protection: bisphosphonates or denosumab reduce skeletal events, with osteonecrosis of the jaw a recognised side effect.
Where the exam tries to catch you
Most traps here involve choosing the wrong investigation or missing a neurological emergency.
- Trap: ordering a bone scan to diagnose myeloma Correct: the scan is often normal in myeloma, so a skeletal survey and serum protein studies are the right tests.
- Trap: treating a solitary lytic vertebral lesion as a metastasis without protein studies Correct: a solitary plasmacytoma needs radiotherapy, and myeloma is excluded by protein studies and marrow examination.
- Trap: missing spinal cord compression from a collapsed vertebra Correct: neurological signs with vertebral collapse are an emergency needing urgent imaging and specialist treatment.
Frequently asked questions
Why is a bone scan often normal in multiple myeloma?
A bone scan is often normal in multiple myeloma because its lesions are osteolytic and do not provoke the osteoblastic reaction that the scan detects. A skeletal survey is therefore the better imaging test.
What are the CRAB criteria in myeloma?
The CRAB criteria are hypercalcaemia, renal insufficiency, anaemia and bone lesions, which define end-organ damage needing treatment in multiple myeloma. Their presence separates symptomatic myeloma from smouldering disease.
How does solitary plasmacytoma differ from multiple myeloma?
Solitary plasmacytoma is a single lesion of clonal plasma cells in bone or soft tissue, without the marrow disease of multiple myeloma. It is usually treated with radiotherapy, but it can progress to multiple myeloma over time.
How is myeloma bone disease treated?
Myeloma bone disease is treated with anti-myeloma therapy together with bisphosphonates or denosumab to reduce skeletal events. Radiotherapy relieves painful lesions, and surgical stabilisation is used for impending pathological fractures.