A thirty-year-old male presented with complaints of painful swelling in the left shoulder region with weakness of all the four limbs.

RADIOLOGICAL FINDINGS:

A plain radiograph of the left shoulder revealed an expansile, trabeculated, lytic lesion arising from the superolateral aspect of the left scapula The lesion produced bulging and thinning of the cortex and had a narrow zone of transition . No periosteal reaction was seen. The glenoid articular surface appeared to be intact. (Fig 1).

Fig. 1

The differential diagnosis considered were : Giant cell tumor, metastasis and solitary plasmacytoma.

Computed Tomography

A CT scan revealed an expansile lesion with cortical thinning associated with a soft tissue Mass (Fig 2, Fig 3).

Fig. 2	Fig. 3

MRI showed a large, multilobulated, expansile lesion in the superolateral aspect of the left scapula involving the coracoid process . It appeared isointense on T1W images, hyperintense on T2WI and shows homogenous postcontrast enhancement. It showed break of the cortex with extensive involvement of the subscapularis and the supraspinatus muscles. Multiple flow voids were seen within it suggestive of tumoral vascularity. Rest of the scapula was normal.

Hyperintense lesion seen within the rotator cuff muscles, represented tumoral infiltration/ lymphatic edema. Minimal fluid was seen in the glenohumeral joint and along the biceps tendon. The glenohumeral joint was normal. (Figs 4-9)

Fig. 4: Transverse T1-weighted spin echo image	Fig. 5: Transverse T2-weighted spin echo image
Fig. 6: Coronal T1-weighted spin echo	Fig. 7: Post-contrast coronal T1 weighted spin echo
Fig. 8: Sagittal proton density fat saturation image	Fig. 9: Sagittal TIRM image

Other investigations

Blood investigations showed normal hemoglobin, erythrocyte sedimentation rate (ESR), fasting and postprandial blood sugar, liver and renal profile.

Urine examination for Bence-Jones proteins and immunoelectrophoresis was negative. Serum protein electrophoresis was normal, but an M band (IgG, l light chain) was seen on immunoelectrophoresis.

Skeletal survey was negative - radiographs of the skull, spine, ribs and pelvis were normal. A CT scan of chest, abdomen and pelvis revealed no other lytic lesions.

EMG studies were consistent with features of peripheral neuropathy.

A core biopsy of the lesion revealed atypical plasma cells; whereas bone marrow biopsy showed 1% plasma cells with no evidence of plasma cell dyscrasia.

Final Diagnosis : Solitary bone plasmacytoma .

This case shows a rare association of solitary bone plasmacytoma with peripheral neuropathy.

DISCUSSION:

Solitary plasmacytomas are tumors composed of monoclonal plasma cells, which are cytologically, immunophenotypically, and genetically identical to those seen in multiple myeloma, but occur as solitary lesions.

Solitary plasmacytomas can be divided into two groups according to the location. If the single tumor originates in the bone marrow , it is solitary bone plasmacytoma. If it arises from the tissues other than bone marrow it is called extramedullary plasmacytoma. Most of these are found in upper air passages and oral cavity.

Incidence:

Solitary plasmacytomas as compared to multipla myeloma are rare representing less than 5 % of the plasma cell dyscrasias.

Age sex distribution :

It mainly affects younger patients. As many as 25% of the patients with plasmacytoma are 30 years of age or younger. It is more common in males . M: F = 4:1

Location :

Solitary bone plasmacytoma tends to involve the axial skeleton and spares the skull and long bones. Over 40% of solitary plasmacytomas are localized in the vertebrae (thoracic spine > lumbar spine ) followed by pelvis , skull, sternum, ribs and scapula. It is interesting to note that the ribs, which are frequent sites in multiple myeloma , are not initially involved in the solitary lesion.

Presentation :

Most patients present with pain secondary to bone destruction by the infiltraring plasma cell tumor. It is commonly accompanied by neurological manifestations , detected in as many as 25 % of cases of plasmacytoma.

A rare presentation of a solitary plasmacytoma is the POEMS syndrome: Polyneuropathy, Organomegaly, Endocrinologic abnormalities (amenorrhea, impotence, diabetes, etc.), M-protein, and Skin changes. It is thought to be caused by cytokines produced by the tumor.

Imaging findings

Plain radiograph:

A solitary growth tends to be larger and more expansile than any individual lesion of multiple disease and is frequently complicated by a pathological fracture.

The spine : A bubbly expansile lytic lesion in the vertebral body causing bulging and thinning of the anterior and posterior cortices. It may resemble the appearance of an aneurysmal bone cyst. Eventually there is cortical penetration and vertebral body collapse.

The pelvis : An osteolytic lesion in the pelvis may take any of the following appearances:
(1) A sharply circumscribed area of rarefaction with or without a sclerotic border ;
(2) Dissolution of a localized segment of cancellous and cortical bone ;
(3) A giant septated lytic lesion with a lobulated sclerotic margin;
(4) A diffuse loss of cancellous bone structure in the entire bone ; or
(5) A generalized miliary type of dissemination throughout the entire pelvis.

The differential diagnosis of these lesions include simple bone cyst , giant cell tumor and metastasis.

The skull : Solitary myeloma of the skull may present as single large area of osteolysis resembling osteoporosis circumscripta or as an expansile multiloculated lytic bony defect involving the inner and outer tables of the skull. It is similar to lesions seen in metastases of thyroid or kidney origin.

Computed tomography :

CT can be used to detect the extent of osseous and soft tissue involvement - especially in areas of complex anatomy such as the spine , shoulder and pelvis.

Magnetic Resonance imaging:

The MRI appearance is consistent with that of a focal area of bone marrow replacement; The signal intensity is similar to muscle on T1-weighted images and hyperintense relative to muscle on T2-weighted images. It tends to enhance somewhat with gadolinium administration. An extraosseous soft-tissue component is often present. Short tau inversion recovery (STIR) sequence may allow detection of small focal collections of tumor that escape visualization with standard spin echo MR imaging methods

Diagnosis :

The distinction between multiple myeloma and solitary bone plasmacytoma is important as therapy for solitary bone plasmacytoma is definitive local radiotherapy whereas therapy for multiple myeloma is systemic and includes steroids, irradiation, and chemotherapy.

Criteria for diagnosis of Solitary Bone Plasmacytoma

1. Single bone lesion - as demonstrated on complete radiographic skeletal survey and CT/MRI scan of the axial skeleton ( skull, spine, pelvis, proximal femora and humeri)
2. Clonal plasmacytosis - seen on the biopsy of the tumor or flow cytometry and immunohistochemistry.
3. Normal bone marrow - lack of clonal plasma cells or aneuploidy on flow cytometry.
4. Absent or low, serum or urinary levels of monoclonal proteins- if present at the time of diagnosis should disappear after 6 - 12 months of therapy.
5. Preserved levels of uninvolved immunoglobulins.
6. No anemia, hypercalcemia or renal impairment attributable to myeloma.



Treatment:

The standard treatment for a solitary bone plasmacytoma is irradiation to the entire lesion with appropriate margins. The dose used in radiation therapy for solitary bone plasmacytoma is typically between 3,000 and 4,500 cGy. Treatment with radiation is associated with cure in approximately 40-50% of patients without evidence of recurrence 10 years after treatment. Both osseous and extraosseous or extramedullary plasmacytomas are treated with radiation therapy. Surgical resection is rarely necessary.

Adjuvant chemotherapy has been administered with inconclusive results. Although some studies have found that adjuvant therapy may prevent or delay progression to myeloma, most have noted no benefit with early administration of chemotherapy.

Prognosis:

While the majority of patients with solitary bone plasmacytoma develop myeloma after a median of 2-3 years, the overall median survival of 7-12 years is longer than for patients in early phases of symptomatic myeloma. Approximately 15%-45% of patients remain disease free at 10 years and although the majority of these appear to be cured, rare late recurrences have been reported.

Hence, after completion of radiotherapy, patients should be monitored regularly. The monitoring should include serum and urine immunofixation, complete blood count, serum calcium, and creatinine every 4 to 6 months for one year, and annually thereafter. Patients should also receive a bone survey or MRI annually or sooner if the patient develops a serum M protein after treatment or an increase in a persistent M protein.

Summary :

Solitary bone plasmacytoma (SBP) is a rare presentation of plasma cell neoplasms. It's association with peripheral neuropathy is all the more rare. In contrast to multiple myeloma, long-term disease-free survival and cure is possible with local radiotherapy (RT). Imaging alone cannot differentiate these tumors from more common malignant entities such as carcinoma, meningioma in cases of intracranial extramedullary plasmacytomas or metastasis from other primaries. The role of imaging should be focused on early detection of additional or recurrent lesions and the presence of regional lymphadenopathy which will influence clinical management.