Ibrutinib Use Complicated by Progressive Multifocal Leukoencephalopathy

: Progressive multifocal leukoencephalopathy (PML) is a fatal demyelinating disease associated with immunocompromised states. We describe a case of PML, which developed after prolonged ibrutinib use and a low burden of chronic lymphocytic leukemia disease. The delay in diagnosis of the patient despite multiple presentations to medical providers across different facilities suggests that there is a lack of awareness of PML as a potential complication of ibrutinib. Treatments with postulated anti-John Cunningham polyomavirus agents and IL-2 were ineffective, likely due to the advanced state of the patient's disease. Although recent evidence indicates that ibrutinib may enhance cell-mediated immunity, consistent with elevated CD4+ and CD8+ T cells and appropriate T-cell response to mitogens in the patient, ibrutinib-mediated inhibition of the humoral function may contribute to PML pathogenesis. As the duration of ibrutinib use is often indefinite, and the number of indications for ibrutinib continues to grow, recognition and further evaluation of the link between PML and ibrutinib is warranted.