solitary bone plasmacytoma

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Solitary bone plasmacytomas is an uncommon plasma cell tumor which is localized to bone. They 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

Solitary bone plasmacytoma is one of the two subgroups of plasmacytoma, the other being the extramedullary plasmacytoma.

Epidemiology

peak incidence is in 4to 6decades
more common in males ~2:1

Clinical presentation

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 is a pain at the site of the skeletal lesion due to bone destruction by the infiltrating plasma cell tumor.

Patients with long bone involvement may present with pathologic fracture.

Diagnostic criteria

Diagnostic criteria for solitary bone plasmacytoma has been considered as follows :

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 anemia, hypercalcemia or renal impairment (usually attributable to myeloma)
low or absent serum/urine monoclonal protein
preserved levels of uninvolved immunoglobulins

Radiographic features

Plain radiograph

Solitary expansile lytic lesion with thinning and destruction of the cortex, and bubbly/trabeculated appearance. Characteristically, the absence of sclerotic reaction is seen.

CT

Expansile lytic lesion with thinned out cortex and characteristic 'mini-brain' appearance has been described in solitary vertebral lesions.

MRI

A mini-brain appearance has also been described on MRI . 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 tumor 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.