Progressive multifocal leukoencephalopathy associated with a lymphoproliferative disorder treated with pembrolizumab

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease affecting the central nervous system as a result of reactivation of the John Cunningham (JC) polyomavirus and occurs almost exclusively in immunosuppressed individuals. The disease course of PML is variable but usually progressive and often fatal. Treatment is predominantly focused on immune restoration, although this is difficult to do outside of human immunodeficiency virus–associated PML. A recent case series demonstrated a potential role for programmed cell death protein 1 (PD-1) inhibitors, such as pembrolizumab, to contain and/or clear JC virus. Herein, we discuss the first reported Australian case of a 61-year-old female with PML secondary to chemoimmunotherapy demonstrating complete clearance of JC virus as well as clinical and radiological stabilisation following pembrolizumab treatment.