Sinonasal Extramedullary Plasmacytoma With Rare Osteolytic Lesions.

Plasmacytomas are malignant tumors characterized by abnormal monoclonal proliferation of plasma cells. They originate either from bone or soft tissue and could be primary or a part of a systemic process during the course of multiple myeloma. Extramedullary plasmacytomas (EPs) in the sinonasal tract or nasopharynx are rare and mostly presented as case reports. We describe a unique case of multiple myeloma involving the nasal cavity and the paranasal sinuses with osteolytic expansile lesions of the first cervical vertebrae (atlas), the clavicle, and the skull in a 51-year-old man. The diagnostic approach was challenging, and finally the biopsy of the extramedullary tumor settled the diagnosis of multiple myeloma. The patient underwent posterior occipitocervical fusion due to upper cervical spine instability due to atlas osteolysis. The patient had an uneventful recovery, and he was finally referred to the hematology department. EP of the nasal cavity is a rare entity and requires a high index of suspicion. EP should be included in the differential diagnoses of nasal cavity masses, especially in males in the age group of 50-60 years. A thorough clinical history, examination, and proper laboratory and radiological investigations are important to settle an accurate diagnosis to initiate treatment as soon as possible. Timely diagnosis ensures a better prognosis and deters the progression of the disease.