Journal of Clinical Oncology, Vol 22, No 7 (April 1), 2004: pp. 1328-1330
© 2004 American Society of Clinical Oncology.
DOI: 10.1200/JCO.2004.05.028
Unusual Presentations of Hematologic Malignancies
CASE 1. Solitary Bone Plasmacytoma: Role of Magnetic Resonance Imaging and Positron Emission Tomography
C.S. Chim,
G.C. Ooi,
F. Loong,
R. Liang
University Departments of Medicine, Radiology, and Pathology, Queen Mary Hospital, University of Hong Kong, Hong Kong
A 53-year-old man presented with sudden onset of upper back pain persisting for 3 days. X-ray scan of the spine revealed collapsed T6 vertebra with ill-defined pedicle (Fig 1). Apart from the T6 collapse, skeletal survey did not identify any bony abnormality. Magnetic resonance imaging (MRI) of the thoracolumbar spine and pelvis showed the collapsed vertebral body of T6 with retropulsion into the spinal canal, and abnormal T1-hypointense and T2-hyperintense signal (Fig 2A). In addition, there were abnormal foci of T2 hyperintensity in the vertebral bodies of T4, T8, T9, and T12 (Fig 2B). Both technetium-99 bone scan and whole-body 2-deoxy-2-(18)fluoro-D-glucose–postron emission tomography (FDG-PET) showed focal uptake only at T6. A mildly hypermetabolic focus of standard uptake value (maximum, 3.1) was detected on FDG-PET (Fig 3). CBC serum albumin, globulin, creatinine, and calcium levels were within normal limits. Serum protein electrophoresis did not reveal any monoclonal band, but immunofixation showed a weak monoclonal band. Serum immunoglobulin G, immunoglobulin A, and immunoglobulin M levels were 1,260 mg/dL (range, 819 to 1,725 mg/dL), 229 mg/dL (range, 70 to 386 mg/dL), and 130 mg/dL (range, 55 to 307 mg/dL), respectively. Bone marrow aspiration showed 7% plasma cells. Immunohistochemistry of the trephine biopsy did not reveal any light chain restriction. Needle biopsy of right T6 transverse process confirmed plasmacytoma and showed infiltration of moderately pleomorphic plasma cells, but mitotic figures were not identified (Fig 4A). Immunohistochemical study showed monoclonal kappa light chain restriction (Fig 4B) but the tumor cells were negative for B-cell marker CD79a, T-cell marker CD3, myeloperoxidase, epithelial membrane antigen, and AE1/AE3. He remained symptom-free for 12 months after local irradiation to the involved sites shown by MRI, at a total dose of 30 Gy, covering T4 to T12.
The diagnosis of solitary bone plasmacytoma (SBP) requires a solitary bone lesion, the biopsy of which shows infiltration by plasma cells; negative results on a skeletal survey; absence of clonal plasma cells in a random bone marrow sample; and lack of anemia, hypercalcemia, or renal impairment suggestive of systemic myeloma.1 Our patient would have fulfilled the criteria of SBP if not for the detection by MRI of multiple other vertebral involvements. The majority of patients with SBP are male, with a median age of 55 years, approximately 10 years younger than those with multiple myeloma.1 SBP may involve any bone, but most often affects the axial skeleton, particularly the vertebra.1 On plain x-ray, SBP usually assumes a lytic appearance. However, MRI is far more accurate in the assessment of the extent of bone involvement.2 On MRI, the signal intensity of SBP is similar to muscle on T1-weighted images, but hyperintense to muscle on T2-weighted scans.2 Our patient had multiple vertebral involvement that evaded detection by skeletal survey. Indeed, previous study has also demonstrated unsuspected lesions on spinal MRI scans in up to one-third of patients with diagnosis of SBP.3 Because of the high cost, MRI should be limited to the spine as part of the staging procedures in plasmacytoma,3 which has prevented understaging in our patient. FDG is an analog of glucose radiolabelled with the positron-emitting isotope fluorine-18. Metabolically active cells take up and phosphorylate FDG, but it is not metabolized further and remains trapped in the cell.4 The intracellular accumulation of FDG is imaged with PET, higher uptake is seen in tumor cells which have increased rates of metabolism over normal tissues. Previous studies have shown whole-body PET to be useful in the detection of asymptomatic, occult myeloma deposits not detected by conventional radiological skeletal survey.5 Of note, as many as 25% of patients with multiple myeloma with negative radiological surveys were shown to harbor multifocal lesions on fluorine-18 FDG-PET.5 However, occult vertebral disease was not detected by PET in our patient, probably due to inactive metabolism as shown histologically by the lack of mitotic figures, and thus very low glucose uptake. In summary, our case illustrated the risk of understaging of disease in an apparent case of SBP based on conventional criteria, and thus potentially under treatment.
Authors' Disclosures of Potential Conflicts of Interest
The authors indicated no potential conflicts of interest.
REFERENCES
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3. Moulopoulos LA, Dimopoulos MA, Weber D, et al: Magnetic resonance imaging in the staging of solitary plasmacytoma of bone. J Clin Oncol 11:1311-1315, 1993[Abstract/Free Full Text]
4. Carrasquillo JA: Clinical indications for FDG positron emission eomography scanning, in Cancer: Principles and Practice of Oncology, Vol 15, No. 10, New York, NY: Lippincott Williams and Wilkins Healthcare, 2001, pp 1-16
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