Plasma cell myeloma or multiple myeloma is a plasma cell neoplasm that is usually associated with synthesis of a monoclonal immunoglobulin (a paraprotein), a monoclonal immunoglobulin light chain (Bence Jones protein) or both [1–4]. In a minority of cases, multiple myeloma is non-secretory. Disease is mainly medullary (i.e. within the bone marrow cavity) but extra-medullary lesions also occur (extra-medullary plasmacytoma). In the World Health Organization (WHO) classification, multiple myeloma is designated ‘plasma cell myeloma’.
Most plasma cell myelomas develop in patients with a non-IgM monoclonal gammopathy of undetermined significance (MGUS). Myeloma affects almost exclusively adults. Clinical features can be the direct effect of the proliferation of plasma cells (e.g. bone pain, pathological fracture, spinal cord compression) (Figure 25.1), can result from marrow infiltration (anaemia) or can be caused directly or indirectly by the paraprotein (hyperviscosity, peripheral neuropathy) or the Bence Jones protein (renal failure). Some cases are complicated by amyloidosis, the amyloid being formed from altered light chains. Organomegaly is usually absent except in patients with extramedullary plasmacytomas or amyloidosis. Lytic lesions are seen by imaging in greater than two thirds of patients. Patients with smouldering (asymptomatic) plasma cell myeloma lack specific myeloma-defining features and amyloidosis. The disease may be stable for many years; the rate of progression to overt plasma cell myeloma is estimated to be about 1% per year. Patients with solitary plasmacytoma of the bone or other tissues such as upper respiratory and gastrointestinal tracts or lymph nodes (extra-osseous plasmacytoma) present with solitary lesions with absent or minimal bone marrow infiltration by plasma cells; end-organ damage attributable to a plasma cell proliferation is absent .
Vertebral collapse in multiple myeloma.
Haematological and pathological features
Anaemia is usual. Thrombocytopenia occurs less often. A blood film characteristically shows increased rouleaux formation (Figure 25.2) and increased background staining (a blue tinge to the blood film), as a result of the presence of a paraprotein; patients with synthesis of Bence Jones protein only or with non-secretory myeloma lack these features and less often have hypercalcaemia or impaired renal function. The erythrocyte sedimentation rate is characteristically elevated in patients with a serum paraprotein. Sometimes there are circulating neoplastic cells. When these account for >20% of total leukocytes or >2 ×109/l in absolute numbers, the designation of plasma cell leukaemia is used  (Figure 25.3). However, these thresholds for a diagnosis of plasma cell leukaemia have been questioned since the adverse clinical impact of this feature is equally seen at lower levels (>5%) of circulating plasma cells . These patients more often have organomegaly. A leucoerythroblastic picture is seen in some patients.
Peripheral blood film in multiple myeloma showing increased rouleaux ...