Sellar Plasmacytoma: An Unusual Presentation of Anaplastic Multiple Myeloma

Abstract

Abstract Background: Anaplastic multiple myeloma (AMM) is an extremely rare morphological subtype of multiple myeloma that has been reported only sporadically. Furthermore, pituitary involvement by multiple myeloma is rare and can be misdiagnosed as a nonfunctioning pituitary adenoma, due to its radiological and clinical similarities. Clinical Case: A 46-year-old man with no past medical history presented with a 3-month history of left shoulder pain. Initial physical exam revealed a large left neck mass, which prompted a left shoulder x-ray remarkable for left supraclavicular mass. Chest CT scan showed a bony mass (7 x 4 x 4 cm) in the left anterior second rib with extra osseous soft tissue involvement. CT also noted left supraclavicular/infraclavicular and left axillary adenopathy. Patient also reported lightheadedness and double vision for a few months and found to have diplopia with upward gaze on exam. Brain MRI revealed uniformly enhancing mass in right sphenoid sinus involving the sella measuring 2.3x2.6x3.2cm. With exception of low Hemoglobin (10.5, 13.5 - 17.7 g/dL) and mildly elevated prolactin (29.9, 2.0 - 20.0 ng/mL), laboratory testing was within normal limits including complete blood count, metabolic panel and pituitary hormone levels. Patient underwent fine needle aspiration of the supraclavicular node, which showed anaplastic plasma cell neoplasm. Further work up noted elevated M-spike, Kappa light chain 92.7 (0.3-2.0 mg/dl), kappa/lamda ratio 23 (0.3-1.6) and beta-2 microglobulin 4324 (600-2,200 ng/mL). Bone marrow biopsy confirmed 70% myeloma involvement with kappa monotypic plasma cell population expressing CD20, CD138, CD38, and CD117. Patient underwent endoscopic endonasal trans-sphenoidal biopsy of the mass. Frozen section pathology revealed a plasma cell neoplasm, and a subtotal resection was performed. Final surgical pathology confirmed anaplastic plasma cell neoplasm. He was started on systemic chemotherapy and external beam radiation. Conclusion: Sellar involvement by myeloma is very rare with less than 50 cases reported in the literature. While rare, these tumors should be considered in the differential diagnosis for lesions involving the sella as the therapeutic approach is different from other sellar masses. While the radiographic appearance can be similar, pituitary plasmacytomas typically present with headache and neurological signs such as cranial nerve palsies and visual changes, with preserved pituitary function. Close attention to physical exam and lab parameters can provide clues to this rare diagnosis.