Solitary plasmacytoma of clavicle: A case report

Introduction: Plasmacytoma is a localized collection of malignant plasma cells. The disease can be divided into solitary plasmacytoma of the bone (SPB) and extramedullary plasmacytoma (EMP), both of which are distinct entities. An EMP, the rarer of the two, has soft tissue infiltration by clonal plasma cells without any occult or systemic myeloma. Whereas, SPB has a solitary lytic bone lesion with infiltration of monoclonal plasma cells, with absence of the same on a random marrow sampling or any evidence of systemic myeloma. Though SPB may involve any bone in the body but involvement of medial end of clavicle, though reported, is extremely rare. Case Report: Herein, we report a case of a 65­year­old farmer presented with pain and swelling of the medial end of the left clavicle, which was postoperatively diagnosed to be a solitary plasmacytoma by virtue of histopathology and IHC, with no other evidence of osteopenic lesions on radiographs, a negative bone scan, absence of marrow involvement by monoclonal plasma cells, presence of M­band on serum protien electrophoresis, in the IgG region and no evidence of anemia, hypercalcemia, hyperuricemia, hypercreatininemia, nephropathy, respiratory and urinary tract infections that can suggest the presence of any systemic myeloma. Conclusion: The case of solitary plasmacytoma of the clavicle reported here is a very rare as a disease entity, and rarest because of the site of involvement. The patient was treated with surgery and radiotherapy and had excellent disease control.


INTRODUCTION
Solitary plasmacytoma of the bone (SPB) comprises only 3-5% of all plasma cell neoplasms [1]. The new world health organization (WHO) criteria define SPB as a solitary lytic bone lesion with infiltration of monoclonal plasma cells, with absence of plasmacytosis on a random marrow sampling, with absence of any evidence of systemic myeloma (renal insufficiency/ anemia/hypercalcemia) and a negative bone scan; along with a monoclonal gammopathy on serum protein electrophoresis.
The SPB more commonly involves the axial skeleton, with an active marrow, as in vertebra, ribs, skull, pelvis, femur, clavicle and scapula relatively sparing the appendicaular skeleton [1].
Primary bone tumors and tumorlike lesions of clavicle are uncommon, comprising only 0.45% of the total, and their occurrence is more likely to be malignant, than benign [2,3] . We hereby present a case of SPB involving the clavicle, which is rare as per the disease entity and rarer because of the site involved.

CASE REPORT
A 65yearold male farmer was presented with a two month history of swelling and a month old pain, increasing on exertion, around the left shoulder, with loss of appetite for the same duration. The lump was initially the size of a lemon, before it progressed. Clinical examination revealed a hard nontender lump on the medial end of the left clavicle 4x5 cm with restricted shoulder mobility. There were no palpable nodes. Radiographs of chest showed a lytic expansile lesion involving medial onethird of left clavicle associated with a soft tissue mass in the apical region of the chest (Figure 1).
A plain noncontrast computed tomography (CT) scan of the neck and thorax is shown in Figure 2.
(i) Normal CT scan of the neck, (ii) Soft tissue density lesion with bony expansion and erosion of medial end of left clavicle with adjacent soft tissue density lesion and no evidence of rib crowding bone biopsy suggested, (iii) Fibrotic strands in both upper and right lower lobes.
(iv) Simple liver cyst. Ultrasonography of the whole abdomen showed a simple cyst in right lobe of liver. Blood counts, liver and kidney function tests were normal except for serum LDH 725 U/L. Bone marrow examination revealed anemia of chronic disease, with no evidence of plasmacytosis or secondary deposits.
Fine needle aspiration of the clavicular lump revealed a malignant mesenchymal neoplasm, possibly spindle cell sacoma with lymphoplasmacytic infiltration. Independent review of the slides too, did not reveal the presence of any abmormal or immature plasma cells, probably because of sampling error or error in terms of slide preparation or preservation ( Figure 3). The patient then underwent an excision of the left clavicular lump. The postoperative histopathology showed the presence of a plasma cell neoplasm, comprising sheets of immature plasmacytoid cells, admixed with a few mature plasma cells (Figure 4). Immunohistochemistry (IHC) showed expression of CD 138 and CD 38, and are immunonegativity for cytokeratin, CD 56 and CD 20, confirming the diagnosis to be of plasma cell neoplasm. The IHC for immunoglobulin light chain was not done.   Serum protein electrophoresis showed the evidence of monoclonal gammopathy in the IgG region. There was no Bence Jones protien in urine. Serum calcium was 9.2 mg/dL with albumin 3.8 g/L, Xrays revealed no evidence of any other lytic bone lesions, the whole body bone scan was negative, and no evidence of urinary tract or respiratory tract infections.
This patient was then treated with postoperative radiotherapy. At the third month of followup the patient is doing well with almost full range of movement at left shoulder joint and normal daily activities.

DISCUSSION
Primary bone tumors and tumorlike lesions of clavicle are uncommon. Klein et al. presented a series of around 1300 primary bone tumors and found that only 0.45% of them involved the clavicle [2]. In a review of 35 primary bone tumors of the clavicle that have been treated at the Memorial Sloan-Ketterin cancer centre, Smith et al. reported only five benign lesions [3]. Primary bone tumors of the clavicle are therefore more likely to be malignant than benign. Solitary plasmacytoma of the bone accounts for 10-30% of primary chest wall malignancies. They are more common in male patients and usually occur at mean age of 60 years or later. The most common chest wall location is ribs, clavicle, sternum [4]. Considerable debate exists regarding the relationship of SPB and EMP to multiple myeloma. Most authors believe that SPB is simply an early presentation of multiple myeloma whereas others consider that SPB is a clinically distinct entity [5]. As far as treatment is concerned excision remains the mainstay of treatment, where ever possible. Radiotherapy has also shown to be successful for local control of solitary plasmacytoma [6]. However, chemotherapy is recommended to patients with disseminated disease and evidence of progression following the primary modes of treatment. This case is extremely rare, and the patient had an excellent disease control with surgery and radiotherapy. Longterm followup will be necessary for our patient as 35-55% of patients of SPB, might end up developing multiple myeloma over a period of 10-12 years from initial diagnosis [7].

CONCLUSION
We reported a case of solitary plasmacytoma of clavicle which is a rare disease, presenting in an extremely rare site. The diagnosis was confirmed by clinical suspicion, postoperative biopsy, immunohistochemistry, and other investigations relevant to rule out the presence of systemic myeloma. The patient was treated by surgery followed by radiotherapy. As per world literature this is the standard of care. The patient had excellent disease control, and is currently undergoing followup. *********

Author Contributions
Aruj Dhyani -Conception and design, Drafting the article, Final approval of the version to be published Abhash Shankar -Analysis and interpretation of data, Drafting the article, Final approval of the version to be published Arunima Gupta -Acquisition of data, Critical revision of the article, Final approval of the version to be published Rupesh Kumar -Acquisition of data, Critical revision of the article, Final approval of the version to be published Koushik Chatterjee -Conception and design, Critical revision of the article, Final approval of the version to be published Anup Majumdar -Analysis and interpretation of data, Critical revision of the article, Final approval of the version to be published

Guarantor
The corresponding author is the guarantor of submission.