Intracranial Involvement in Multiple Myeloma Presenting as a Cranial Nerve Palsy

Multiple myeloma (MM) is characterized by the neoplastic proliferation of plasma cells producing a monoclonal immunoglobulin. Neurological complications in MM most frequently occur due to spinal cord compression by bony lesions, paraprotein-related neuropathy, hypercalcemia, hyperviscosity, or amyloidosis. Intracranial involvement is a rare complication of MM occurring in only 1% of patients. It can manifest as a solitary cerebral lesion, intra-parenchymal infiltration, or diffuse leptomeningeal disease. We present a case of a leptomeningeal myeloma in a 71-year-old woman with known relapsed MM presenting with a right sixth nerve palsy. Our patient was receiving spinal irradiation for a paraspinal plasmacytoma when she complained of double vision. Clinical exam revealed a right sixth nerve palsy. MRI revealed diffuse abnormal leptomeningeal thickening and enhancement typical for diffuse leptomeningeal infiltration. She was treated with whole brain irradiation and intrathecal methotrexate combined with a lenalidomide and dexamethasone chemotherapeutic regimen but unfortunately she passed away 5 weeks after onset of visual symptoms. MM involving the central nervous system (CNS) is a rare complication of MM and carries a poor prognosis with an average survival of 3 months. Due to its rarity, treatment of CNS MM is very heterogeneous. Thus case reporting is important to accumulate data on this rare presentation.