Multiple myeloma with bone marrow extracellular crystal deposition

Plasma cell dyscrasias are a heterogeneous group of disorders characterised by the expansion of a single clone of immunoglobulin secreting, terminally differentiated, end-stage B cells.¹ Many of their clinical and morphological features are the result of the production and accumulation of excessive amounts of monoclonal immunoglobulin. Intracellular inclusions, both intracytoplasmic (Russell bodies) and intranuclear (Dutcher bodies) are occasionally seen in bone marrow biopsy specimens from patients with plasma cell neoplasms, and less frequently in reactive states.^2,3 Extracellular protein deposition also occurs, although less frequently. “Myeloma kidney” with tubular casts composed of a heterogeneous mixture of electron dense homogeneous material and Tamm–Horsfall protein, together with elongated crystals, some with a fibrillar or lattice substructure, is an important cause of myeloma-associated morbidity and mortality.^4,15 The formation of extracellular crystalline structures within the cornea, skin, thyroid gland, intravascular space and bone marrow along with other sites has been described.^5–9 However, this phenomenon is unusual and is limited to isolated reports. In our department, we see approximately 1200 bone marrow trephines per year, including about 300 cases of multiple myeloma, and they have not previously come to our notice.

Description of case

A 72-year-old man presented with back pain. A spinal x ray carried out six months later showed collapse of the first lumbar vertebra. Further investigations included haemoglobin 9.3 g/dl, creatinine 129 μmol/l, calcium 2.5 mmol/l, β2-microglobulin 3.9 mg/l, IgG …