Multiple myeloma presenting with cavernous sinus syndrome: A case report and literature review

A 68-year-old man presented with progressive left cranial nerve III palsy, initially misattributed to a vascular etiology. Early magnetic resonance imaging revealed a mass in the left cavernous sinus with extensive calvarial lesions. Concurrent serum studies, including serum protein electrophoresis and free light-chain assays, identified hypercalcemia, renal dysfunction, anemia, bone lesions features, and a monoclonal Immunoglobulin A lambda spike, leading to a diagnosis of multiple myeloma with central nervous system involvement manifesting as cavernous sinus syndrome (CSS). The patient responded rapidly to corticosteroids and palliative radiotherapy, followed by systemic chemotherapy. This case illustrates the critical role of early neuroimaging and comprehensive serum studies in diagnosing CSS due to multiple myeloma and emphasizes the need for heightened clinical suspicion when evaluating atypical cranial neuropathies.