Asymptomatic premalignant plasma cell/lymphoplasmacytic proliferative disorder characterised by a serum monoclonal protein of < 30g/L, < 10% plasma cells on bone marrow biopsy, without associated end organ dysfunction (hypercalcaemia, lytic skeletal lesions, renal dysfunction, anaemia and hyperviscosity).
3 major types:
1. Non-IgM MGUS (G, A, D, E) - most common. Risk of progression to smouldering myeloma and symptomatic myeloma; less frequently progresses to AL amyloidosis, light chain deposition disease or another lymphoproliferative disorder.
2. IgM MGUS - risk of progression to Waldenström's macroglobulinaemia (asymptomatic then symptomatic); less often progresses to lymphoma and AL amyloidosis.
3. Light chain MGUS (LC-MGUS) - may progress to idiopathic Bence-Jones proteinuria and to light chain plasma cell myeloma, AL amyloidosis or light chain deposition disease.
Affects approximately 1-2% of adults. Mean age of 70 years. Most cases are sporadic, though there is evidence that first degree relatives of patients with MGUS have a higher incidence of myeloma, lymphoma or Waldenström's macroglobulinaemia.
Usually encountered when patients are screened for a variety of other disorders/symptoms.