Orbital Plasmacytoma as Initial Presentation of Multiple Myeloma.

Multiple myeloma (MM) is a hematologic malignancy characterized by clonal proliferation of plasma cells in the bone marrow. It represents approximately 10% of hematologic malignancies and is the most common primary bone malignancy. This disease usually occurs between the ages of 40 and 70, although it is more frequently seen in patients over 65 years of age. On the other hand, extramedullary plasmacytoma-related diseases have a global annual incidence of three per 100,000 people. Orbital involvement in MM is considered rare. Orbital plasmacytomas represent less than 1% of all orbital lesions, and their incidence in relation to MM is approximately 3%. Only 35% of cases present the initial manifestations of MM.  In the following case we present a 63-year-old male patient who presented with left ocular proptosis of one month's duration, along with intermittent thoracic and lumbar back pain as well as weight loss of 12 kg in five months. A non-contrast cranial CT scan revealed a 31 x 31 x 36 mm extraconal orbital mass in the left orbit, with invasion of the paranasal sinuses and intracraneal extension, in addition to multiple lytic skull lesions. Laboratory results included severe normocytic normochromic anemia, mild thrombocytopenia, chronic kidney disease stage G3b, hypocalcemia, hyperphosphatemia, and elevated alkaline phosphatase. Immunohistochemistry demonstrated infiltration by clonal plasma cells (CD138 + and kappa +), findings consistent with MM.