A Rare Presentation of Extramedullary Plasmacytoma Localized to the Base of the Tongue With Abnormal Lymph Nodes: A...

Solitary plasmacytoma is a localized form of plasma cell neoplasm and is important to differentiate from multiple myeloma (MM) using clinical assessment, imaging, and bone marrow evaluation. Extramedullary plasmacytoma (EMP) develops from soft tissue and is a rare occurrence, although a large proportion of cases are in the head and neck. We describe a 59-year-old man who presented with a progressively enlarging left-sided neck mass. Imaging revealed a lesion in the left tongue base and supraclavicular and cervical lymphadenopathy. Biopsy of the left tongue base lesion revealed mature plasma cell proliferation, with positivity for CD79a, CD138, and CD38, a low Ki-67 proliferative index, and lambda light-chain restriction. Whole-body positron emission tomography-computed tomography (PET-CT) also revealed hypermetabolic disease at the base of the tongue and the nodes, and bone marrow evaluation was negative for systemic disease. After multidisciplinary review, a diagnosis of primary EMP of the left tongue base with regional nodal involvement was made, and the patient agreed to radical radiotherapy (RT) (50 Gy in 25 fractions over 5 weeks). This case underlines the importance of keeping EMP as a differential in the diagnosis of masses involving the tongue base or oral cavity in the context of cervical lymphadenopathy. PET-CT and bone marrow examination are important for staging and treatment decision-making, and radiotherapy is an important treatment option for localized disease.