The Royal Liverpool and Broadgreen University Hospital, Liverpool, UK

Plasmacytoma is the localised form of multiple myeloma, which can affect any part of the body including the axial skeleton (Kelly et al, 2006; Ampil et al, 1995). These myelomas/plasmacytomas arise from one malignant clone of cells, which secrete the same type of immunoglobulin. Where the clone of cells remains localised, it is known as plasmacytoma, but when there is spread of the malignancy to multiple bones and marrow, it is known as multiple myeloma (Boccadoro and Pileri, 1995).

We present a case of solitary sacral bone plasmacytoma (SBP), in a seventy year old man which presented as low back pain, following a fall. He was neurologically intact, and had no sphincteric incontinence, but MRI revealed a large expansile lesion in S1, which caused severe spinal stenosis, involving the left L5 exiting foramen, with an irregular area of low signal posteriorly. Bone scan showed increased tracer uptake in L5 and a mixed hot/photopaenic appearance in the mid-sacral region indicating tumor involvement. Myeloma screen confirmed that the serum IgA was high, with positive kappa monoclonal band, positive Bence Jones Protein (BJP), normal IgM and IgG, and normal calcium profile. CT-guided biopsy revealed sheets of mature plasma cells, consistent with the diagnosis. Fine needle aspiration biopsy of an enlarged groin lymph node revealed neoplastic infiltration, consistent with myeloma. Skeletal survey and CT chest/abdomen/pelvis (CAP) were not contributory. The patient had six courses of radiotherapy and improved remarkably, and is being considered for chemotherapy as well as follow up in the out-patients' department.