Central nervous system involvement in plasma cell neoplasms: a rare presentation illustrated by three cases.

Central nervous system (CNS) involvement in plasma cell neoplasms is rare and associated with poor prognosis, and indications for cerebrospinal fluid (CSF) analysis remain undefined. We describe three cases: two with advanced-stage, high-risk cytogenetics, and one stage I case meeting criteria for plasma cell leukemia (PCL). In two patients, delayed CSF evaluation after neurological symptoms led to rapid deterioration, whereas early CSF analysis in an asymptomatic patient enabled timely diagnosis. One case worsened acutely after treatment with plerixafor. These findings suggest that CSF evaluation may merit consideration in high-risk patients, including those with PCL or before plerixafor administration.