Clinical Course, Risk Factors, and Therapeutic Response in Multiple Myeloma with Central Nervous System Involvement

Extramedullary disease (EMD) is increasingly recognized in relapsed/refractory multiple myeloma (MM), with central nervous system involvement (CNS-MM) representing a rare but highly aggressive manifestation associated with dismal outcomes. Data on its incidence and optimal management, particularly in the era of cellular and bispecific therapies, remain limited. We conducted a retrospective analysis of MM patients with pathology-confirmed EMD treated at our institution between January 2000 and December 2023. CNS-MM was defined by parenchymal or leptomeningeal involvement. Clinical features, cytogenetics, treatments, and outcomes were analyzed, with predictors of CNS involvement evaluated among EMD patients. Among 304 patients with EMD, 20 (6.5%) had CNS-MM. CNS involvement occurred a median of 19.2 months after MM diagnosis, though 15% presented at diagnosis. CNS-MM was strongly associated with high-risk cytogenetics (OR 3.7) and additional visceral EMD (OR 4.6). Median overall survival from CNS-MM diagnosis was 4.2 months. Outcomes were significantly improved in patients receiving CAR-T cell therapy or bispecific antibodies, with a median OS of 19.2 months versus 1.2 months in those who did not receive immune effector therapies. Intrathecal chemotherapy demonstrated limited and transient benefit. In conclusion, CNS-MM is an aggressive complication enriched in high-risk, multifocal EMD with extremely poor prognosis. Cellular and bispecific therapies show promising activity and may meaningfully improve survival, whereas intrathecal therapy appears to have limited efficacy. Prospective studies are needed to define optimal treatment strategies for CNS-MM.