CASE REPORT: THORACIC PLASMACYTOMA AS THE INITIAL PRESENTATION OF MULTIPLE MYELOMA

Introduction
Plasmacytomas are plasma cell dyscrasias that can develop in bone or soft tissue. These findings might be solitary or, more commonly, associated with multiple myeloma (MM). Nearly 7.0% of MM cases present a plasmacytoma at the time of diagnosis.
Clinical Case
The patient was a 77 years-old male. He was diagnosed with monoclonal gammopathy of undetermined significance (MGUS)/smoldering (asymptomatic) MM 10 years earlier. Upon diagnosis, protein electrophoresis identified a monoclonal peak of M protein <3.0 g/dL (IgA/kappa), bone marrow aspirate had 4,0% of plasma cells, and bone marrow biopsy had 10-15% of plasma cells with monoclonal characteristics. No organ-lesions were identified. As such, the patient was attending a hematology consultation every six months for monitoring. At one of such consultations, the patient complained about left chest pain at the supramammary region (three weeks of evolution). There was no history of trauma or any other relevant symptoms. Analyses showed an unchanged monoclonal peak of M protein (<3.0 g/dL), kappa/lambda ratio of 2.86, and lack of cytopenias, hypercalcemia, kidney failure, hyperproteinemia or hypoalbuminemia. A chest x-ray revealed a conspicuous opacity in the left pulmonary hemifield. Computed tomography (CT) showed an expansive mass, invading the parietal pleura at the fifth left costal arch. CT-guided biopsy was performed, and immunophenotypic evaluation identified 82.5% aberrant plasma cells (CD38++, CD138+, CD19-, CD56+, CD45-, kappa). The histological report classified the mass as a plasmacytoma. A bone marrow aspirate was also performed: morphological evaluation identified 5.0% plasma cells, while the immunophenotypic evaluation only identified 1.8% plasma cells (97.0% of which were abnormal). Positron emission tomography (PET) demonstrated several lytic lesions, mainly across the axial skeleton, and on the left costal grid. Given the clinical findings, the diagnosis of MM with an associated thoracic plasmacytoma was established. The patient underwent chemotherapy and radiotherapy, which stabilized the progression of the disease. After five months of follow-up, anemia (11.3 g/dL) is the only analytical abnormality, and bone disease is the only organ-lesion to register. Two major complications occurred so far: 1) non-traumatic left femoral neck fracture; 2) exudate left pleural effusion (1800 mL), with 8217 cells/μL (86.0% abnormal plasma cells).
Discussion: In this case, the most relevant clinical finding is the thoracic plasmacytoma. Upon diagnosis, there were doubts about its classification. Cardinal analytical markers of MM were absent, which would support the lack of major bone marrow involvement. Despite this finding, 97% of abnormal plasma cells were found on the bone marrow aspirate. Also, several lytic lesions were detected on PET. As such, solitary plasmacytoma was excluded. Instead, this case portraits a thoracic plasmacytoma associated with MM. Most likely, this complication is the result of the natural progression of MGUS. Therefore, this case reinforces the importance of regular follow up of MGUS patients, as that was fundamental for the early diagnosis and treatment.
Another aspect to emphasise is the role of the cytological evaluation to quickly classify the exudate pleural effusion as a MM complication. That is particularly relevant because immunophenotypic evaluation is not always available.