26th June 2023

Myeloma

In myeloma and other monoclonal gammopathies, renal impairment occurs as the result of the nephrotoxic effect of immunoglobulin light chains. Multiple myeloma is a malignant proliferation of plasma cells. Normal plasma cells come from the B cell line and produce immunoglobulins. Normal immunoglobulins are polyclonal composed of a variety of heavy chains and light chains. In myeloma, plasma cells produce immunoglobulin of a single heavy and light chain, known as a monoclonal protein or paraprotein. The most well-known of these, which occurs in the urine, is known as the Bence Jones protein, which occurs when only a light chain is produced.

Diagnosis of myeloma requires two of the following criteria:

1. Increased malignant plasma cells in the bone marrow (>10%)
2. Serum or urinary paraprotein
3. A myeloma defining event (remembered by the mnemonic CRAB):
   • C – Calcium: hypercalcaemia
   • R – Renal: Renal involvement
   • A – Anaemia: low Hb
   • B – Bone: lytic bone lesions

End organ damage can occur in myeloma, with the kidneys, bone marrow or bones themselves being more susceptible. Renal failure can occur due to paraprotein deposition, hypercalcemia, an increased susceptibility to infection or amyloidosis. Treatment is often with intravenous fluids to treat the renal impairment and is the first line treatment for hypercalcemia caused by multiple myeloma.