Solitary bone plasmacytomas (SBP) may involve any bone, but they have a predisposition for the red marrow-containing axial skeleton:
- spinal disease is observed in ~50% (range 34-72%) of cases
- the thoracic vertebrae are most commonly involved, followed by lumbar, sacral, and cervical vertebrae
- the rib, sternum, clavicle, or scapula is involved in 20% of cases
Peak incidence is in the 4th to 6th decades, and it is more common in males.
Physical findings are related to the site of involvement, presenting as a painful mass, pathologic fracture, or root or spinal cord compression syndrome.
The most common symptom of solitary bone plasmacytoma (SBP) is a pain at the site of the skeletal lesion due to bone destruction by the infiltrating plasma cell tumour.
Patients with long bone involvement may present with pathologic fracture.
Diagnostic criteria for solitary bone plasmacytoma has been considered as follows 1:
- single area of destruction due to clonal plasma cells
- bone marrow plasma cell infiltration <5% of all nucleated cells
- absence of osteolytic bone lesions or other tissue involvement (i.e. no evidence of myeloma)
- absence of anaemia, hypercalcemia or renal impairment (usually attributable to myeloma)
- low or absent serum/urine monoclonal protein
- preserved levels of uninvolved immunoglobulins
Solitary expansile lytic lesion with thinning and destruction of the cortex, and bubbly/trabeculated appearance. Characteristically, the absence of sclerotic reaction is seen.
Expansile lytic lesion with thinned out cortex and characteristic 'mini-brain' appearance has been described in solitary vertebral lesions.
A mini-brain appearance has also been described on MRI 3. It is seen as curvilinear low signal intensity areas within the lesion, giving an appearance of sulci in the brain. In fact, this appearance is so characteristic that it may obviate the need for a diagnostic biopsy.
Signal characteristics include:
- T1: hypo- to isointense
- T2: iso- to hyperintense to muscle
- T1 C+ (Gd): variable enhancement
Treatment and prognosis
Excision of the tumour and its extent is done, with chemo-radiotherapy as an adjuvant. Local recurrence is less than 5% and dissemination is seen in 35-70% of patients. The disease may progress to multiple myeloma, with a bad prognosis.
General imaging differential considerations include:
- 1. Dimopoulos MA, Kiamouris C, Moulopoulos LA. Solitary plasmacytoma of bone and extramedullary plasmacytoma. Hematol. Oncol. Clin. North Am. 1999;13 (6): 1249-57. - Pubmed citation
- 2. Ooi GC, Chim JC, Au WY et-al. Radiologic manifestations of primary solitary extramedullary and multiple solitary plasmacytomas. AJR Am J Roentgenol. 2006;186 (3): 821-7. doi:10.2214/AJR.04.1787 - Pubmed citation
- 3. Major NM, Helms CA, Richardson WJ. The "mini brain": plasmacytoma in a vertebral body on MR imaging. AJR Am J Roentgenol. 2000;175 (1): 261-3. AJR Am J Roentgenol (full text) - Pubmed citation
The differential diagnosis for bone tumours is dependent on the age of the patient, with a very different set of differentials for the paediatric patient.
- bone-forming tumours
- cartilage-forming tumours
- chondromyxoid fibroma
- fibrous bone lesions
- bone marrow tumours
- other bone tumours or tumour-like lesions
- aneurysmal bone cyst
- benign fibrous histiocytoma
- giant cell tumour of bone
- Gorham massive osteolysis
- haemophilic pseudotumour
- intradiploic epidermoid cyst
- intraosseous lipoma
- musculoskeletal angiosarcoma
- musculoskeletal haemangiopericytoma
- primary intraosseous haemangioma
- simple bone cyst
- impending fracture risk