A paraprotein is a monoclonal immunoglobulin or light chain present in the blood or urine; it is produced by a clonal population of mature B cells, most commonly plasma cells

Paraproteinaemia: Paraproteinaemia represents a group of related diseases characterised by an unbalanced or disproportionate proliferation of immunoglobulin-producing cells, usually from a single clone.

Primary paraproteinaemias are caused by a build-up of monoclonal protein (either the full antibody or antibody fragments) in the serum or urine. There may also be monoclonal plasma cells present in the marrow, soft tissue (as in plasmacytomas), or in the circulation.

Epidemiology:

• 3.2% in people aged over 50

Classification

Primary paraproteinaemias can be classified into pre-malignant and malignant types

• Non malignant type: The important pre-malignant type to be aware of is monoclonal gammopathy of unknown significance (MGUS)
• Malignant types:
  • Multiple myeloma
  • Waldenstrom's macroglobulinaemia (WM)
  • Solitary plasmacytoma

Waldenstrom macroglobulinemia (features)

WM is a low-grade lymphoma where monoclonal plasmacytoid lymphocytes in the marrow and organs secrete monoclonal IgM. Clinical features are caused by IgM deposition (hyperviscosity, polyneuropathy), organ infiltration (hepatosplenomegaly, lymphadenopathy), and pancytopenia.

Solitary plasmacytoma (features)

Solitary plasmacytoma typically presents as a tender swelling affecting bone or soft tissue. Biopsy reveals abnormal collections of plasma cells.

Secondary paraproteinaemias

Note that paraproteinaemias are also seen in association with lymphoma (particularly non-Hodgkin's lymphoma) or leukaemia (particularly CLL). These are called secondary paraproteinaemias.