Leptomeningeal Involvement in Relapsed Multiple Myeloma With Thoracic Spine and Orbital Metastases: A Case Report.

Multiple myeloma (MM) is a clonal plasma cell disorder that primarily originates in the bone marrow and rarely presents as extramedullary disease. Central nervous system involvement, particularly in the form of leptomeningeal disease, is a rare and aggressive manifestation of MM. We report a case of a 44-year-old female with relapsed MM who presented with headache, diplopia, and ptosis. Brain magnetic resonance imaging revealed multiple enhancing dural nodular lesions. Cerebrospinal fluid cytology was negative for malignant cells. A dural biopsy confirmed leptomeningeal involvement of MM through histopathological examination and CD138 immunostaining. The patient was managed with systemic and intrathecal chemotherapy and corticosteroids and was referred for radiotherapy. Leptomeningeal involvement in MM remains a diagnostic and therapeutic challenge due to its rarity, rapid progression, and nonspecific presentation. This case highlights the need for heightened clinical suspicion and comprehensive diagnostic evaluation in MM patients with neurological symptoms.