A positive PET/CT after radiation treatment for solitary bone plasmacytoma
A 37-year-old woman originally presented in 2003 with the gradual onset of paresthesias and weakness of the lower extremities that had progressed resulting in significant gait disturbance. An MRI of the thoracic spine revealed a large paraspinal and intraspinal mass of T9 and T10 vertebral bodies causing lytic destruction of the vertebrae with cord compression at T9 and T10 levels. She underwent partial resection of the mass and vertebrae to relieve the cord compression and spine stabilization. Her surgical specimen pathology was most consistent with plasmacytoma of the T9 and T10 vertebral bodies and chronic inflammation suggestive of Castleman’s disease of pleura.
The subsequent work up for the multiple myeloma, including the skeletal survey and the bone marrow biopsy, were negative. She completed radiation therapy with total dose of 4,500 cGy. Her lower extremity strength, neuropathy and gait all markedly improved. The follow-up MRI six months later showed no new lesions except for possible scar tissue at T10 area.
Four years later, while pregnant, she presented with a new right hip pain. Her serum protein electrophoresis showed a new small IgG lambda M-component. Work up for myeloma was unrevealing. Further imaging was delayed because of pregnancy. She was managed expectantly as her hip pain spontaneously resolved. She continued to have a small stable 0.3 gm/dL IgG lambda M-component throughout the pregnancy.
Courtesy of M Ghesani
The subsequent staging PET/CT after delivery revealed 3.7 cm 3 1.6 cm mass with standard uptake value of 14.2 in left posterior 11th/12th intercostal space and left pararenal space, inseparable from the left diaphragm. CT guided biopsy confirmed recurrent plasmacytoma, which on immunohistochemistry was CD138 positive, lambda positive, and CD20 negative. Once again, work up for multiple myeloma, including the bone marrow biopsy, was negative. She underwent a second radiation treatment with 4,500 cGy for her recurrent solitary plasmacytoma. Two months later serum protein electrophoresis still had a small but unquantifiable IgG lambda M-component. Re-staging PET/CT had a grossly stable 3.7 cm 3 1.3 cm soft tissue mass in the same location with decreased standard uptake value of 10.1 from 14.2. Currently the patient is under observation alone.
Solitary plasmacytoma originating in the bone is defined as an isolated lesion comprised of neoplastic cells that produce a single clone of the plasma cells in the absence of other features of multiple myeloma. It is a rare condition and constitutes only 5% of all plasma cell neoplasms. More than 50% of patients with solitary plasmacytoma of the bone will progress to develop multiple myeloma within the course of three to 10 years. The median overall survival of patients is approximately 10 years. The conventional treatment for the plasmacytoma of the bone is radiation therapy. The usual dose of 40 Gy to 50 Gy given for about four weeks produces local response rate of about 80% to 90%.
The prognostic factors for solitary plasmacytoma of the bone whether before of after radiation therapy have not been established. A review of solitary plasmacytoma was conducted by the Mayo Clinic in the attempt to better define the clinical features and gross prognostic indicators of the disease. The review showed that of 46 cases from the clinic 54% progressed to multiple myeloma, 11% developed local recurrence, and only 2% developed new plasmacytoma in the absence of multiple myeloma.
Adverse prognostic factors associated with higher relapse rates were age older than 60, extra-axial skeletal lesions location, and tumors of more than 5 cm. The presence of M-protein at the time of diagnosis did not have a prognostic value; however, after radiation therapy, persistent M-protein for more than one year was a significant predictor of subsequent progression to multiple myeloma.
Courtesy of M Ghesani
A series of 60 patients evaluated at M.D. Anderson showed that persistent M-protein was the only independent factor that was associated with adverse outcome. The researchers recommended that patients should be monitored frequently and considered for chemotherapy treatment when they either develop symptoms or show an increase in M-protein level.
Later, the risk stratification model developed at the Mayo Clinic identified two predictors: 1) persistent serum M-protein level > 0.5 g/dL, and 2) abnormal free light chain ratio at the time of diagnosis. The model established a five-year progression risk of 13% for low risk (zero), 26% for intermediate risk (one) and 62% for high risk (two).
In the era of PET/CT, with regard to staging for plasma cell neoplasms, a potential prognostic factor may be the presence of the persistent FDG activity after definitive radiation therapy. A very small series of 11 patients who had pre- and postradiotherapy PET/CT showed complete metabolic response in eight patients, progressive disease in two patients and one patient, who initially had no response, eventually developed a late response. Persistence or slow resolution of FDG activity may play a role in the prognosis of the solitary plasmacytoma and it certainly warrants further studies.
Liana Makarian, MD, is an Oncology Fellow at St Luke’s-Roosevelt Hospital.
Munir Ghesani, MD, is Associate Clinical Professor of Radiology at Columbia University College of Physicians and Surgeons and Attending Radiologist at St.Luke’s-Roosevelt Medical Center.
Michael Grossbard, MD, is a Professor of Clinical Medicine, Columbia University College of Physicians and Surgeons.
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